Just for the sake of hearing all the sides to this conversation, I would like to ask one time that an MKV NOT be released. There is just no reason for it, and in the long run it will hurt the project by dividing the pool of sharers between virtually identical files.
The problem I see is that you would be releasing two identical video/audio streams. That means instead of having 100 seeds sharing the file on a torrent, you will have two files with 50 seeds. For the health of the project and its longevity I think a single unified release is the best option. VLC plays .m2ts files. To remux a .m2ts to .mkv takes a single command (mkvmerge 00000.m2ts -o deed21.mkv) and a couple minutes. I don't see a situation where a person would be able to play the mkv but not be able to work with the avchd. I do see situations where a person could play the avchd but not the mkv. If the audio and video feeds are identical, and there are no menus, there is no reason to release the exact same file twice in two different containers. Why not release it as an .mp4? Why not ogg? At some point you just have to say it doesn't make sense to release the same file in every container. If people want .mkv, just add 3 lines to the readme explaining how to remux .m2ts to .mkv. No sane person would release a work as .rar, .zip, tar.gz, and .7zip.
That is the equivalent of what people are asking of you. "I like rar better than zip. Release as rar because I already have winrar installed." "No, release as zip, windows has native zip support." It is a silly debate, and I think it is perfectly clear why you would not release something as both a rar and zip.
Everyone has to understand that this project serves a much larger audience than the tech literate. If you only release one file type, half the community will complain that they want the other one. I think an ISO is a more understood filetype than MKV for people who don't understand technology. Any computer with burning software knows what to do with an ISO. IMHO it is more "idiot proof." To the person that does not know what they are doing "insert blank disc, double click file, press burn, stick disc in blu-ray player" is as about as simple as it can get. Trying to get grandma to use tsmuxer or multiavchd is an uphill battle. If you are using MKV, presumably you are already a tiny bit tech literate. Unpacking an iso and copy/pasting a command into the command prompt should be easy as pie. Heck you could even include mkvmerge, and 7zip, and a batch file and have a one click avchd2mkv converter.
I vote for now to JUST release the AVCHD and keep the community united instead of fragmented. It will allow the file being passed around the web to remain healthier. Hold off on the blu-ray until whenever you like, as it will be nearly identical video quality anyway.
If I could make a request, it would be for a TRILOGY BLU-RAY once you are done. Since each avchd .m2ts file is 7gb, that means you could get ALL THREE on a single 25GB BD. That would mean simple menus and no bonus features, but I think it would be awesome to have a single disc with all three movies. It would also be the easiest way to share physical copies with people and not overwhelm them. One disc, one case, one trilogy.