My issue with the dragon decor is mostly in principle. There's no barrier to making the decor available through both SP and MP, unless the SP dragons don't have skeletons or something.
And still... not everyone plays on PC or considers a elite account necessary for their gaming, so they couldn't play MP if they wanted to without shelling out further. This is a lousy thing to do when we're talking a single player game from a developer that's been making single player RPGs (and cultivating that fanbase) for the better part of two decades.
The connectivity argument is a moot point for those not online, they either don't even know about the content or may not even care about the content at that point. Access to it is again usually a choice if they are willingly choosing to not be online.
Not to mention, since it is DLC content, it becomes the same situation of items found in other DLCs like Wardens Keep or Golems or something from Origins. The only time they got that content in the end was re-buying the double pack that was released a few years back with the DLC in it for Origins. So if the choice is you don't want online capabilities or what not, you don't really have a right to complain about things, you made that choice and the DLC offers rewards if you want it.
A shaky example of what I mean. My laptop will never be able to Play Witcher 3, and apparently the PS4 version is terrible, so i'm stuck not playing that for a while, but that is my choice. I'm not going to complain about it with CD Projekt Red for focusing on PC over console, or making their games look so good I need a huge rig to make it run because I can't afford that high end PC on my teacher salary. It's the nature of their model in the end. Nothing to do with multiplayer, but moreso my enjoyment of a game people seem to like a whole lot, which kinda sucks.
Now, for those who just cant get online, that is again another problem, and mostly a modern one on how games are being developed now a days. That there is little I can say to make that better, but thats an industry-wide issue, not just a BioWare issue.
Regardless, if people don't want to play multiplayer when it is their choice, frankly, you only get to complain if the game is forcing you to play the multiplayer for something huge that either affects the game, or is a gateway to actual story content. You say on principle the decor is a problem, I say if you want and can get it, then the only one stopping you from doing so is yourself. There are no principles at risk here because the content is extremely negligible.
If you said the ending to Inquisition was locked behind multiplayer...then I agree with you. That is the difference i'm arguing.