There are already a few actively maintained forks of Tachiyomi. TachiJ2K and TachiyomiSY are two such popular forks which have several features not present in the original app. In fact, many hardcore manga readers in the community had already switched to them years ago. There’s also Aniyomi, which not only supports manga but also watching anime via extensions, the same way you’d read manga in Tachiyomi.
So thanks to the power of FOSS, Tachiyomi already continues to live on and you don’t need to wait for a fork.