I didn't really want it until season 6, only because it took me a veeeeeery long time to figure out r+L=j and I didn't know shit about asoiaf so I also didn't know where each character was going or who was more important than who.
it's not just a matter of practicality (of course that is important) they are also just...perfect for each other. once/when/if Dany finds out that Jon is her brother's son, I think that will make her want to be even closer to him.
about the dragons though, I think these are gonna be the last dragons I don't think any of them will survive till the end. as for the lightbringer bullshit, yeah i think and hope that is just bullshit I thought GRRM cares little about prophecies?