This guest post is by Eliot Van Buskirk of music app blog and database Evolver.fm.

On one level, Spotify’s transformation into a music platform was a simple technical matter of exposing an application programming interface (API) to app developers and publications and allowing them to treat Spotify like a web browser for their HTML5 apps, linking each song to Spotify’s catalog. Big whup, as we used to say.

As GigaOm points out, at least one developer fears users might “forget about [his app]” within the Spotify platform.

However, every developer we spoke with at the event was enthusiastic about adding their app to Spotify, even though Spotify apps are desktop-only (for now) — and even though, due to the intricacies of dividing the loot with labels, publishers, and Spotify itself, developers can’t charge for or include ads in these apps (for now).

Even Spotify’s director of product development, Charlie Hellman, thinks these app developers will eventually be able to charge for their apps.

“I think the potential for people to build a business on the Spotify platform will happen over time,” he told us. “This is day one, really, of us transitioning from being an app to being a platform.”

With that in mind, here are some key snippets from Evolver.fm’s interviews with developers at Spotify’s “music platform” announcement yesterday:

MoodAgent founder and CEO Peter Berg Stephenson

“[Over the long term] a lot of app developers will see the monetization opportunities [within Spotify], because they won’t happen in the short term within the client, for the simple reason that [Spotify has] all these dependencies on the labels, who actually take the biggest cut of anything that happens on screen.”

“I know that a mobile version of this is in the making. And, of course, there are a number of ways we can monetize — either by driving new users to Spotify [Premium], and get a rev[enue] share from that, but much more interestingly, with a large volume of users, we know the mood that people are in at a specific time and a specific place, and we can use that information to drive partners to… services matching the mood to their product… or brand values… You can imagine Coca-Cola being interested in knowing that it’s a happy user [to whom] we’re showing this ad for their product.”

Fuse vice president of marketing Joe Marchese

“We’re a television company, so there are some interesting roads to go down inside of the Spotify app, because it’s HTML5. And because we’re a television company, we’re one of the few that can have on-air stuff kicking to our Spotify application. So, you’re watching our weekly top 20 countdown and on television, in the bottom, people can be in influencing it in Spotify… every two weeks, we’re going to be looking at rolling out new features, or as much time as Spotify will put up with us.”

“I know it’s easy to get carried away on the launch day, but it’s huge. Spotify is one of the pre-eminent music players in the world right now. Things are starting to funnel through them. People have access to music [there] but they don’t necessarily have the curation, so with a 24-hour linear television station, we curate all day long… This, for us, is: If the entire music community is here, and we can provide a filter or lens through which to view it, that’s huge for our linear television.”

Songkick founder Ian Hogarth

“I think it’s a really big deal. We’ve been brainstorming with Spotify for ages about how this could happen. We’ve been talking about it at Hack Days and trying to come up with the right way of doing it… Spotify users have been asking for it and our users have written in saying ‘integrate with Spotify,’ so it’s something we know there’s a lot of pent-up demand for.”

“What’s so exciting to me is the level of seamlessness. In a single click, Songkick will scan all the music in your Spotify playlist and build you a personalized calendar of every single concert [from those bands] in your city… [Or] say you’re going to Singapore on holiday [great, because we at Evolver.fm are always going on holiday to Singapore]. You can bring up the city listings, and say ‘I’m free on Wednesday night.’ There would be a list of bands, and half of them you’d never have heard of. You can now, with the click of a button, listen to that band right there within the listings. It’s kind of like the Village Voice with a play button on it… I think it’s going to have a great impact on artists’ livelihoods and fans’ lives.”

We Are Hunted CEO, founder, and “tech guy”

“Our site’s been growing tremendously in the last six months, we think we’ve got a great product, and we can be one of the best music discovery services in the world if more people knew about is. That’s what this is about for us.”

“Spotify has only spoken about the desktop. I assume it’s going to go to mobile at some point, and it’s all HTML5, so it’s easily portable to that.”

“We met the guys from Spotify before who came from Skype, and they were talking to us about the parallels they saw in the fun brand, the peer-to-peer architecture, the growth he saw at Skype, and the Swedish origin — [they're] seeing it happen all over again, and he’s expecting they’ll blow up. We put a bet on Spotify. We’ve been approached by all these guys to do charts and stuff, and then two years ago, their creative director, who’s now at Facebook, reached out to us and said “I love Hunted, I love the idea of it, can you guys be in there?’… we had 18,000 followers [in Spotify even before this app]. We just had a bet at one point that discovery is going to be a big differentiator between these guys, MOG, and Rdio, and we want to be there… It took a year longer than we thought. They had to wait a year to come into the US, but now [that] they’re here, it all made sense to us.”

TuneWiki CEO Larry Goldberg

“There are going to be a lot more people who haven’t heard of TuneWiki before who are going to find out about what we offer, and how passionate we are about lyrics. We’re thrilled to be able to allow Spotify users to have the lyric-viewing experience. The other thing is, as you know, our lyrics, database, and syncs are crowdsourced… so to have people who use Spotify become part of the TuneWiki community as well, to add syncs and lyrics into the overall database will be fantastic for us.”

“We’ve been providing lyrics to people who have stored [music] libraries for some time, and as the business evolves, it’s clear that people are also going to use on-demand services… partnering with one of the leaders in that area helps us move the bar forward… You have to start somewhere.”