Ignoring consumer products for a moment: we've done this at my company for an internal app. Our legacy system was built as a desktop app for internal uses that

Ignoring consumer products for a moment: we've done this at my company for an internal app. Our legacy system was built as a desktop app for internal uses that became difficult to both scale and comply with our regulatory obligations, so we began buildin out an api around its core business functionality and built various front ends to speak with it throughout our company. It has been a middling success, mostly because change requires political capital that might not be there six months to after initiating it. However I think overall we've improved the product and I don't think a massive rewrite would've gone nearly as far due to political winds shifting and the rewrite getting deemed a waste of time by the new new powers that be.