2. We switched to DBAL, but we don't use query builders yet, so doubt you can switch to another driver without havibg to modify a bunch of queries.
3. Ewan did some work with React and Angular. I think the lesson learnt is you have to throw away the view system and start from scratch to make it work.
4. We are fully compatible with PHP7. HHVM is not fully supported - there are some failing tests, but I imagine there isn't much work to have it all fixed.