I have yet to be brave enough to use any of the amazing custom extensions built by the community. I am just not quite comfortable with it.
But I am seriously considering it. Would all the current custom extensions be compatible once Wappler 8 is released in the next year?
A slight correction? THIS year! 
Unless a new version of App Connect is not backward compatible, the AC extensions should work, and because most are server agnostic, they will work in any project (PHP, .NET, ASP, NodeJS).
The same should be true for Server Connect extensions, keeping in mind that these are dependant on the server model that they are based on..
Heads-up: If all goes well, I'll be presenting a video tutorial on the subject in the upcoming Meetup on Friday 12th June.
If there are any issues with any of mine i will fix them but as they are straight forward .js and json, i dont see any reason. Some have worked effectively since version 5 with no issues.
Custom extensions are basically built in exactly the same way as the Wappler team develop components so if extensions break, no does Wappler!