I'd like to suggest a couple of feature improvements, if possible.
First, it would be great to have a video preview feature. This is especially useful for multi-angle Blu-rays, where the on-screen text can vary depending on the region or language (this is very common with PIXAR releases). Since the multi-angle option doesn’t specify the language or region, a preview would help identify which version you're exporting to MKV.
Secondly, I’d Love to see a subtitle preview as well. In many cases, tracks are labeled as “forced subtitles,” but they’re not actually forced. Usually, there's one full subtitle track, one for audio description, and one that’s truly forced.
Having previews like this would avoid the need to export everything to MKV and then edit it later with MKVToolNix or similar tools. The same goes for video previews — they would help avoid multiple export attempts.
Thanks a lot for reading!
Best regards.