First off you are looking at this from a mathematical theoretical viewpoint. The 2.0L Ecoboost is not considered the superior engine. Though it has more displacement there are several negatives that have just been pointed out. If you want to upgrade its Turbo you will need an adapter and that is more expensive . Second off the intake valve coking you consider minor maintenance is actually expensive maintenance as you have to take the intake manifold off the head to clean those valves.
The 1.5 on the other hand is downright amazing. It puts out slightly more hp than ours stock it come with direct and port injection stock. They are tuning them in the UK to 260HP on stock fueling and nothing more. Just a fricken tune. The engine has a lot of potential , Oh and did I mention the 3 cylinder has a really cool engine note similar to a 6 cylinder.
I have done engine swaps in the past as I used to own a RB25DET( Nissan Skyline 2.5L turbo 6 cylinder) in a 240sx . Its eaiser to swap a smaller engine into the car than a larger one. Not that the larger swaps have not been done (LSX I hear you in the corner yelling at me. )
Though ya the more fascinating swap is indeed the 1.5 in my opinion. Plus whatever engine you are gonna swap you will have to port over the ECU so the amount of wire work to do the swap is the same.
Sure from I am a cheap ass I just want to swap in more HP the 2.0L might be the what seems logical swap( I told you to shut your mouth LSX swap.) The 1.5 swap would be way more interesting and higher in the possible cool factor scale.
Truth be told total more swaps are a pain in the but either way . Ya LSX just pipe down. Unless its an older car even then wiring will be done.