I’m not super familiar with Soundslice. But all the tab users I know use guitar pro or maybe ultimate guitar, and none of them can read standard notation on its own. Does Soundslice have a lot of tab-first users?
Yes, Soundslice has a ton of tab-first users. And in fact the primary reason I founded the site was to scratch my own itch of being able to create tab that's synced with real audio recordings. (I'm a guitarist myself.)
When I read the blog post, I thought it was saying that Soundslice didn't have any tab support.
The comparison of "we expect this (classical notation screenshot) but instead got this (ascii tab screenshot)" made me think that the only thing Soundslice supported was classical notation.
Definitely a subtle distinction there. Soundslice supports tab in many formats (MusicXML, Guitar Pro, PowerTab, TuxGuitar, PDF/images of published tab, or tab notated directly in the Soundslice editor) but didn't support ASCII format yet.