AVS to MKV?

I've been making DVDs for several years, and have a nice workflow from Avisynth to HCEnc and GfD.

Now I've got a TV that can directly support MKV, so I'm looking to produce those.

I would like to keep using Avisynth scripts as my source, as if I'm going to reencode a video I like to tweak the filters.

What options are there?