So, what is your solution?

Should new apps be denied from maemo repos until they have been tested with titans kernel? What if the developer is not interested in overclocking and cannot be arsed to do this? His/her (otherwise fine app) will never appear in repos? What if tomorrow we will get a neat unofficial kernel from Paul, and another one from Mary? Apps now need to be tested with all four available kernels before allowing them to repos?

No, that is nonsense -- that kind of control is possible only among components of a closed system. The only sensible way to do it here is the one that was practiced: develop and test with the official kernel, official components. If there are problems with community add-ons, fix them as problems appear, if feasible.