Will a mk7 age as well as a mk4 NO. Common rail engines do not age as well as rotary pump engines. Injectors cost almost ten times as much money as ALH ones which are everywhere to be found. The ALH has proven not only good to 400k but past 700 with minimal maintenance. I own both, the 2015 is new with only 10k. Having had a 2014 before and the amount of engine noise that developed in 90k I would not have much faith in it being as reliable and cheap to own as a mk4. I have faith in the engines lasting, but at great cost when it is time for injectors and such which ARE a maintenance item in the lifetime of the vehicle. The court ordered warranty is a great thing so long as VW stands behind it and we all know that they do not...
My suggestion if you do go mk7 invest in better filtration on the fuel system (2 micron filter PLUS water block filter) and frequent oil changes, say 10k intervals instead of 16k. Try not to shut it down when regenerating (several apps and such available to watch the egt through obd2 port).
Depending where you live with emissions testing (or not) could also be a big factor, in Ontario deletes are not going to happen...I suspect moving forward these cars will be under closer inspection at testing time.
The rest of the car is not more complex, it is still a pretty basic car underneath with a rear beam suspension. Front sway bar links will be constant problem, DEF system will likely be a problem as they are on all other modern diesels. At least the front fenders are now plastic...