I think this article is unreasonably lumping together the concept of covers and remixes. Cover songs are covered by compulsory licenses in the U.S.A. These are very 'mechanical' and you can in fact obtain them for virtually any recorded song at a fixed rate. It is possible that companies like Soundcloud may be streamlining the process or helping the publishing rights holders but there is not much preventing covers from being created.
The situation for remixes is much different. Remixes inherently involve the use of a PERFORMANCE, not a composition. Licensing is as you mention in the article very difficult and is up the discretion of the rights holder. If there are platforms that want to reduce friction here I think that is great, but the artist should still have discretion in how their performances are used.
There are two main copyrightable entities in music. First there's the publishing side, which covers the song's actual composition. Second, there's the master side, which, once the song is recorded by an artist, covers the recording.
In statue, you can freely cover any song, and there are royalties baked in. This is covered on the publishing side. There's the mechanical, which covers each duplication of the new recording. There's also the performance royalty which is paid every time there's a public performance (on the radio, in a bar, at a venue), and are administered in the US by the Performance Rights Organizations (ASCAP, BMI, SESAC). There are disputes about these payouts where digital and terrestrial radio are concerned, but that's a whole other thing. Checkout some of the recent congressional panels for a crash course in consent decrees and the other wonderful things each side is fighting about (Pandora vs. ASCAP + BMI, mostly).
Concerning remixes, this gets into the master side. There are no rights written into statute that concern the master side. This is likely due to the major label's continuing influence over the process. As soon as you take a master recording (or the stems therein) and alter it in a DAW or elsewhere it's transformed into a derivative work. In order for it to be legal to sell this work you need consent from all of the stake holders, that is, you need permission from the master rights holder(s) and the owners of the publishing (original songwriters). This is, right now, an ad hoc process. There is no industry agreed upon standard for payment, mostly it's people making it up as they go. I have a general rule of thumb: if there are more than 3 writers on the publishing side, it's not getting cleared. This generally holds in my experience.
Any platform that hopes to solve these problems needs to have end to end consent from all of the rights holders before offering a path to monetization of the derivative, or else you're opening yourself up to litigation. The music industry, as we've seen, is endlessly litigious.
Well I had to think about that quite a bit, because in a very broad sense, they can overlap from an "audience" perspective. Also, I don't think a large majority of amateur musicians take much of any time to get into basic rights management concepts until, well, a hard lesson shows up. Lumping the two together at least - this is my rationalization - brings up that both of them DO entail rights considerations. It's not the dark local club scene of trading riffs and dying young anymore...
The other reason to talk about both of them in the same breath is that both avenues are ones that intelligent, diversified labels will want to exploit whenever possible. Fan culture and engagement is a touchy prospect, and going to SoundCloud and Dubset (iTunes & Spotify) as "partners" rather than "enforcers" is simply smart PR. If that means, haha, blurring the lines about what "up front" rights need to be secured when otherwise having no say in the matter, I think for once the industry is catching on.
You may not agree that these are valid reasons to put the two in tandem, but I think they are and that's why I put it together as a topical - sound though not specific overall - review of what the "traditional" and potential "new" rights avenues might be like.
The situation for remixes is much different. Remixes inherently involve the use of a PERFORMANCE, not a composition. Licensing is as you mention in the article very difficult and is up the discretion of the rights holder. If there are platforms that want to reduce friction here I think that is great, but the artist should still have discretion in how their performances are used.