Personally, I think that R20 characters has probably supplanted the app. But note that that is just my personal feeling and is not based on any messaging from R20. R20 characters can be opened in any browser, mobile or desktop, and any sheets that are r20 characters enabled are at least minimally usable with it without any adjustments to code (except for some edge cases that are only used in some very advanced legacy sheets). As a sheet author, the problem with the R20 app was that there was pretty much no way to test character sheets to make sure that your styles and code would work in the app. Since R20 characters runs with the same processes as a normal r20 game, just on whatever screen the user happens to be using, the code needed for a mobile friendly character sheet on r20 characters is both easier to test (just resize the character sheet while writing the code), and much simpler to code (just basic css media queries for screen size). That of course doesn't mean that a lot of sheets have been set up for a mobile view on r20 characters, but even for those that haven't, they can be used by zooming in on the part of the sheet you are interested in and interacting with them that way.
