I have sort of felt like all the effort I put into my extensive catacombs is wasted...since haulers are the only (living) dwarfs who get to appreciate it.
Then again, I've also thought it would be an interesting mechanic for viewing tombs to generate a bad thought....or at least a possible bad thought based on personality type.
I mean...other than tombs, you can stick coffins in the dining rooms, or in people's bedrooms if you want, and it doesn't really have an effect. It can actually increase value. Tombs right now are just another way to piss your dwarves off by not doing something right.
What? I was sure my dwarves got unhappy thoughts if I tried to make their bedroom also be their tomb. Something about not liking coffins in their sleeping area. I have to try this out.
I don't really understand the bit about tombs just being another way to screw up. Building a good necropolis is always a good time for me. The flavor is engaging, as this isn't the temporary living space of a minor official, but the eternal monument of a great leader(unless I hate the guy, in which case it's a garbage dump--still gratifying though). The potential problems for screwing it up are generally less severe, as pathing to a tomb isn't a major issue.
So maybe Reliquaries, being things of art and beauty, could always generate happy thoughts. Pet coffins could generate happy thoughts. But skulking around in the crypts? That shouldn't put your average dwarf in a good mood (unless perhaps it's engraved? But even then it should be a depressing experience to hang out in the fort's crypts.)
It would add an incentive to actually think about cemetery/crypt design beyond how many walls you do/don't provide each coffin, and plan how it actually relates to your traffic flow. I always bury my crypt way deep on its own route so no one has a reason to go down there. It'd be nice to be doing that other than for the joy of it.
Personally, I line the entrance hall with the tombs of the great dwarves of the fortress, so that visiting diplomats can see the stately resting places of our forefathers. These are not just gravemarkers, but monuments to the men whose bones are interred within, and to the industry and artifice of the fortress.
Plus, the long, wide, low-traffic hallway is a great place to put traps.
The less important dwarves are entombed along the sides of widened exploratory shafts, for a nice catacomb-y feel.
Making dwaves depressed by the sight of a run-down grave, or the grave of a friend might be acceptable, but to make all graves offend all dwarves on sight is really limiting.
Personality and culture should at least mitigate the chance of a dwarf being bothered by graves. That way you can assign burial and corpse hauling to macabre dwarves, who are less deeply effected by it.
I wonder how this could potentially interact with the new burrows system. Maybe you could define a crypt burrow, and a whole slew of new functions and mechanics could be attached to it. Thoughts affecting dwarves who enter that burrow, events within a burrow - Zombie dwarf uprising! - weather affects within a burrow like fog and mist, a little troop of crypt keeper dwarves who just do burial, who "don't really care about anything anymore", and have axe skill so they can keep the zombie population under control. Tons of potential.
I don't see how designating a burrow as a crypt would make undeath more likely. In cultures where undeath was considered a problem, proper burial procedures where generally intended to deter it, rather than induce it.
All in all, I think that anything that makes tombs more interesting and diverse is a good thing, but most of these mechanics can be added to the existing tombs. If the features get added in, and it still feels like a distinct reliquary object is needed, then we can worry about it.