I believe your question is for the ruby core team, so probably it is best to let
nobu or shyouhei or anyone else from the core team who would like to comment.
Personally I think what you described above, provided that it is what is then
changed (have to match the proposals to the actual changes :) ) is IMO fine.
Some of the code/the files is probably very old. Perhaps the core team may
see this as an opportunity if someone takes a closer look at the code.
The last point seems a bit more challenging. For that having benchmarks
available may help - see discussions about jemalloc on the tracker here
for example and proposals by byroot and others about other parts of making
parts of ruby faster/more efficient.