"Typst Overleaf" sounds like a fine business idea to me, if you give the user the option to export TeX (so that they can then submit it to a journal).
(If you support both LaTeX and Typst, and improve the Overleaf experience somewhat -- which is definitely possible -- I can't imagine you wouldn't steal some market share from Overleaf.)
(If you support both LaTeX and Typst, and improve the Overleaf experience somewhat -- which is definitely possible -- I can't imagine you wouldn't steal some market share from Overleaf.)