It is going to be available in LTM as well as M mount - two versions of the same lens.
Larry Cloetta posted a link to the Japanese Voigtlander website which explicitly shows the LTM version:
https://www.cosina.co.jp/voigtlander/vm-mount/heliar-40mm-f2-8-aspherical-l-l39/
It even says L39 in the URL and in the description, so unless something happens and it's cancelled, that's pretty solid confirmation.
That 28/3.5 is one of my favourite lenses of all time. The earlier 28/1.9 in LTM was great - a proper speed king - but felt way too big on a Barnack, and I wasn't ever that impressed with the results. The f/3.5 version balances better, fits better, and produces gorgeous images. I think the two Voigtlander 35mm lenses in LTM, the f/1.7 Ultron and the f/2.5 Color Skopar, are good analogs for that pair. I've never used either one, but the 35mm Color Skopar certainly looks a lot like the 28mm version in build and results, so I'd say the "line" was already complete in that regard.
I was led to believe that producing LTM lenses is way more difficult than making M mount ones, and that the only reason Voigtlander started with LTM was because there was still a patent on the M mount. But Voigtlander definitely have experience with LTM, and I'm glad to see they're going back to it. I just hope it's not a one-off.