Hi Johannes,
It is indeed possible to use LDAP group permissions with SVN when using it with Apache (which is how I've always run it).
I'd be happy to help with that.
Running SVN would give us access to the wonderful SVN::Notify, which I've attached a screenshot of.
And just as a reassurance for the IEM option, I've found SVN to be pretty light on resource use. There are only a few developers committing on any single day here.
Cheers
Luke