Tachiyomi will no longer be actively developed. It may continue to work for you for the foreseeable future but there will be no support for it nor the official extensions.
R.I.P tachiyomi, I have used it for years. Kind of sad to see it go. Are the forks also abandoning development ? I have been using the TachiJ2k fork for the past 3 years or so.
TachiyomiSY will still be actively developed. No idea about J2K but I read somewhere that the dev will implement third party repo support sometime next week so I guess that's a sign.
I use SY and I get the sense that Bobby is more of a fast and loose type while the Mihon dev is focused more on polish. My assumptions are based on the unpolished nature of SY features and the Mihon dev saying "some of us liked plain Tachiyomi" [sic].
I just downloaded TachiyomiSY before a week and I liked how it was better than TachiyomiSY in feature wise. I think Bobby is a dev who focuses more on features aspect. So if the other dev focuses on user interface, I hope it might be a good pair.
more options are definitely good if the developers are different, i hope the devs aren't burner out by developing two applications serving the same purpose.