Version 12.09 of OpenWRT is running really well on my TL-WA801ND access points and in the meantime the OpenWRT project is working on the upcoming version named “Barrier Breaker”. I ported this version to the TL-WA801ND v2 as well and it is also running fine.
If anyone is interested in this I uploaded the required patches here and a precompiled firmware binary here. The precompiled binary provides the same feature set as the one for version 12.09 does. In case that you wish to compile it your own you need to retrieve commit c3e1e1cb2f09ebc8c35455f2ff77061f937dfb05 (r37917) from the OpenWRT git repository in order to get the patch applied without error. I.e. issue
git reset --hard c3e1e1cb2f09ebc8c35455f2ff77061f937dfb05 after cloning the repository.