This is the first time I heard of Sublinks, and honestly after a quick look through here in Lemmy I get the impression that main devs of Lemmy and Sublinks can work together to improve what it is currently the best option (Lemmy).
I honestly think it is way too early to have a Lemmy "replacement" even if it is all running in the Fediverse, I just think it is a split of efforts, granted, I don't know all the background that runs behind and it seems like Sublinks dev does it like a hobby too.
Regarding moving communities to Sublinks, yeah, it is up to instance maintainers, but that is a no for me, heck, I already had to recreate my stuff from the dead FMHY account I had (there was no account migration at the time), it seems like adding more decentralization to me, and we already had that with multiple repeated communities ¯\_(ツ)_/¯
Finally, don't get me wrong, options and alternatives are always welcome in my book, but as I said before, it feels like way too early for me.
The thing is, sublinks lead developer tried to work with development team of lemmy. It was like pulling teeth constantly and his experience was overall negative.