The fact that a lot of features are currently missing is the exact reason why they haven't migrated any pre-existing wikis yet. However, they will be doing that as features become available. As of the last timeline estimate, most/all wikis will be using the new platform by the end of 2020.
As for why they rolled the new platform out for new wikis, that is a whole discussion that staff and users are already having. In favor of rolling it out:
- Most new wikis don't require advanced features; so not having them isn't a huge issue
- It gets new communities/users introduced to the new platform so it isn't a surprise to them when pre-existing wikis migrate later
- It provides pre-existing users an opportunity to get used to the new platform before their communities get migrated
- It allows further refinement of the new platform through collection of actual performance data and user feedback
Points that have been raised against rolling it out:
- It is still not developed enough; more testing should have been done before rolling it out
- Even if there aren't as many features, there shouldn't be this many obvious bugs
- New users should not have to deal with bugs and changing features
- Since they are new, they may not even know what is a bug and what isn't
- Since pre-existing users haven't had time to test it out, how does the community help new users who want to do this and that? It is the blind leading the blind.
- With so few features ready to go, users are probably going to create a new wiki and then be disappointed when they find out they can't replicate a design they saw on an older wiki.