I have the same question. The original RowExpander actually has memory leaks in it if you put other Ext components in it. Mikhail added fixes and I added more on top of that so it works extremely well in 3.x.
Now I've seen lots of threads pop up about its use in 4.x, but it's obvious many of those users are still blindly working from the original plugin with all its issues. I wish they would start with the latest version I posted so everyone can benefit. This would be a lot easier if it was brought into the ExtJS source...
Cleaning up the grid's plugin/feature/subclass strategy is on my list of things to do once we have the new performance improvements doing what they need to do. I suspect that all of the grid features/plugins will be unified into the framework itself (I can't see why not)
You guys are awesome! I'll be looking forward to it!
I finally started to take the leap and upgraded most of my interface to 4.x. The last component to tackle is the RowExpander. I already spent time getting it to work once in 3.x. It's looking harder than I expected to upgrade it to 4.x and, because it is a user extension, it looks like this will be a repeated waste of effort.
It looks like the performance issues have been largely nailed down. Things are looking much better than the last time I checked! Now do you have a better view now of when this RowExpander functionality can be integrated into core ExtJS? Especially one that supports Ext components inside of the expanded row. I'm hoping I may have missed something on this front...