Hi,
I can't speak and don't know well beta wikiversity but for wikisource there is a some good arguments for keeping it. As both closure are often cite together I'd like to give some explanations here (rather short, don't hesitate to ask if you ant to know more).
First, Old Wikisource (historical name, but « Multingual Wikisource / mulwikisource » is more and more used) is not just a incubator but a central hub, a bit like the meta for wikisources.
Wikisources has very specified tools and extensions that are specific to Wikisource (first and most importantly the Proofread Extension - with its 2 specific namepaces - which is used for 94 % of
fr.ws texts, 97 % of
pl.ws, 50 % of
it.ws, etc.). It's not undoable but moving
mul.ws to incubator would require a lot of technical works to avoid breaking basic things (and we only have 2-3 devs who know how Wikisource works).
Multilingual wikisource is quite active (and not just of incubation - althought it's the main activity - but for meta centralisation too). And Wikisource dynamic is very different from other project, ad no activity is not a bad sign ; the basic unit of work is a book and it can be completely finished unlike Wikipedia article, Wiktionary entry, Commons cat, etc.
Finally,
mul.ws precedes Incubator and precedes all Wikisources, Wikisource was a multingual project between 2003 and 2005 ; there is a fringe movement for re-uniting again all the Wikisources on
mul.ws (it probably will never happen but I think it's a nice goal and along the way a lot of efforts are done for internationalisation and mulculturalisation of Wikisources tools).