I've installed noVNC on a Pi before, didn't try accessing it through an iPad and I don't recall if I was using desktop or just terminal, BUT, I think something

I've installed noVNC on a Pi before, didn't try accessing it through an iPad and I don't recall if I was using desktop or just terminal, BUT, I think something like noVNC could get you close to iPad-as-RPI-screen. Add in some VPN functionality and you can keep the Pi running at home, but use the iPad anywhere you can get online (though now you're getting into diminishing returns).