The Write.as guys have been working on a good alternative with their Snap.as service [0]. It's tied to the blogging side, but looks like it'll be another simple tool that doesn't pull the same signup-wall crap as Instagram.
Just a little feedback: as someone not deep in the blockchain world, I have no idea what Blockstack is, or why nothing happens when I click "sign in" or "start writing now". The page does a good job of describing the product benefits, but it doesn't cover square 1 and describe what I need in order to actually start using the product.
Otherwise I know this was a fun project, but it always helps to hone in on your audience on the landing page. Answer, Who's going to appreciate this the most?
It's not about 100% purity. Just not doing this one little, tiny, fundamental-to-their-entire-business thing.