Sadly it's time to say goodbye to the JoomlaBamboo templates, I too have a lot of clients using the BuildR template, and Zentools2 - a great combination. I'd love to see them both updated for J!4
I think I'll miss ZenTools2 the most as it was so much more flexible than JA ACM, it didn't require data to be located in a bunch of different places, everything could be done using Articles which was great for clients to manage their own content.
I've started using the T4 Framework as an alternate although I'd love to find something a little more light weight and open source. I tried using Asteroid but way too much code and again content fragmentation from using Page Builder etc.