User blog comment:Big the cat 10/A Veteran Admin’s Concerns Regarding FANDOM and UCP/@comment-40097997-20200825161755/@comment-26939652-20200827055244

Just think about the time invested by the team into migrating. They've done nothing else since at least December last year. Do you really think they can get that investment back just because they get "free upgrades" of the core wiki software?

Think about it. 10 months developer team hours. In addition adapting to a new code base (cause whether it's custom or not, they knew the code). Then dealing with compatibility layers. Dealing with things that degrade performance because of the number of wikis on Fandom, which is an uncommon pattern. Rewriting the customizations you really need and still maintaining those ("but we're on the same codebase" - moot point - it's still a custom plugin).

Don't just easily buy in to the "Legacy is hard to maintain" or better yet "Being on par with wikimedia is better". It's easy to think that way, but reality is a lot more refined.