The idea behind Forge+ is to be able to create Aleph One maps within Unity, so having it edit OBJ maps would defeat the purpose, unless I’m missing something big here. That said, Weland already has an OBJ exporter to write Aleph One maps to OBJ format, although I haven’t tested it.
There’s also no point in reconverting the M1 maps to M2 format; it’s already been done several times. The conversions bundled with Aleph One 1.0 were probably as faithful as you can get in M2 format (see link below), and there’s no point in wasting your time doing it again. (I would not recommend playing M1 this way – there are too many differences in behaviour between M1 and M2 for it to be a faithful experience. However, it’s probably acceptable for just testing stuff in Unity.)
Now, if you want something like EMR 1.0, Phoenix Rising, Operation Tantalus, or Noah’s Ark in Aleph One format, you’ll have to do those yourself. (There’s already an M2 port of Trojan as well. There’s also EMR 2.0 and 3.0, but those are both way different from EMR 1.0.)
I should also mention the abandoned MUnity project, which seemed to have gotten to a fairly impressive state before being abandoned. https://github.com/Trichosurus/munity If you’re serious about wanting to get Marathon running in Unity, it’s worth taking a look at, especially since Forge+ has also built on MUnity (and Weland). If you can save yourself work by building on others’ accomplishments, I’d advise doing so, since it reduces the likelihood that you burn yourself out before completing the project. (The one caveat is that, since MUnity and Forge+ are both GPL, that does mean you’re required to release derivatives of them under the GPL or equivalent terms as well.)
