Here's a thought: In the section of your Inbox which holds notifications, could you perhaps include sites you have requested to join, and the status?
There are two sites I have requested to join, and I have heard nothing for a few weeks now.
This is a nice feature request, thanks!
In the meanwhile, you can go to the site in which you requested membership,
and visit the Site Members page.
You will see the status of your request there.
Noam \ MyHeritage Team