SSDs do that already for NTFS... It will wait until the disk is idle for a while, then parse the partition table, and then the actual filesystem on the partition itself, to find out which blocks are no longer pointed to by any files. And then, it will erase those blocks. That seems like a really really bad idea to me, but then, nobody asked me.
All this, just so that the OS doesn't need to support TRIM...
Quick google search also finds:
"Samsung controllers with recent firmware take an entirely different approach. Without any interaction from the OS, the Samsung firmware is able to 'read' the drive data in the background. When the drive has been idle for a period of time, the firmware reads any NTFS volume bitmaps present and automatically frees up flash blocks not allocated by that partition."