Bring v3 improvement to v2?

[benechiu]

v2 is nice and stable and v3 features are really useful especially the new navigation menu bar and search engine (combining tag search and full text search). Everyone is looking for v3 but it may not be ready in coming 12 months (I guess). Does it make sense to bring some v3 ready features to v2 if the work is not that much (like 1-2 week)? Or we can create a pull request for this?