Being able to use the landscapes in unity or unreal engine would probably alter the whole job sector of game level designers, esp. outdoor scene specialists. Then the price would be way too low. Look at adobe how they cash in with photoshop., on a monthly fee basis. A further alternative would be if you provide it with a sciptable rendering engine, so people can use it to make games, but only with your licensed engine (eg. sales-dependent royalty). I must admit, it's tempting to use your tool for level design.
I used to us Photoshop...since version 3, iirc (yeah, I'm old). Use PS and Adobe products up until they started to do the "CS stuff" and hinted at 'subscription'. I got out then. It wasn't easy...PS was THE program to use for what I did (worked at a print shop as a digital photo 'toucher-upper'; what is called "Photoshopping" nowadays).
Now though, and for years, I've been using Serif....now "Affinity" programs. Check them out if you want a Not-Photoshop-Photoshop program. Affinity Photo actually does a lot of stuff BETTER than Photoshop. Affinity Photo is really starting to be a thorn in Adobe's side from the looks of things. Affinity Photo ('photoshop'), Affinity Designer ('illustrator') and Affinity Publisher ('in-design').
Just FYI if you were looking for a single pay, own forever, PS-Alt. :)
Thanks. These days I use the free version of Artweaver (tho, it has a weird 17 seconds "initialization" pause when run), which substitutes PS 5 pretty well. I miss the .dss export plugin (intel or nvidia) tho, so I also have paint dot net, which is actually pretty good. And then there's Gimp and PhotoGimp. It's a miracle Adobe is still in business.