Development: No, I'm still worried. When I asked in the FotF Toady seemed completely uninterested in any active countermeasures. The best I can hope for is my own assassination missions of villains, and I have the same fear of digging invaders: they get better while my tools to deal with them remain the same, although I have some slight hope for squad orders that might occasionally be followed (i.e. things like "hold the line", "retreat", and so on).
It can also be noted that Toady is notorious for leaving half baked "temporary" measures behind (see e.g. the petition screen, which is completely devoid of most of the relevant info, including the most commonly used name of the petitioner). Sure, the new development style might result in an improvement of feature quality from "barely functional" to "functional".
Mandates are incompatible with my play style, since there's a decade or so with too much work and too few dorfs at embarks with no metal when the morons demand some completely useless metal objects, they just won't stop, and have random (important) dorfs mutilated over retroactive export bans when you FINALLY had a break to get rid of that pile of (non metal) junk with a caravan.
Booby traps would work, as you can set them to be triggered by citizens (but not visitors; GRRR!), but, again, that means the items will be locked away. You'd also need a way to disable them when storing new items, but it could work if current thieves have been dealt with, assuming there are any dorfs left in the fortress. When it comes to wearables, I don't know how to order dorfs to wear trinkets (I know it can be done with DFHack, but not vanilla).
If you want to make a multi racial fortress you need visitors. Apart from me not having any dependent sites, I thought you could only request dorfs (at least it seemed to be the case in 0.44.12). I don't care much about the skills of new citizens, as that can be trained.
Strangely enough, I'm among the small minority that doesn't have a major problem with the stress system. It's unbalanced, and I'd like it reworked, but in 0.47.04 I've only had one petitioner crack, and that was after having been a citizen for a few years. The moron was stressed over not getting laid, and then spent literally every other action on chasing the mayor, and most of the rest on hauling his old junk clothing. Needless to say, he didn't have any friends: that part doesn't seem to have improved visibly.
The guilds I've had have been completely useless, with dorfs milling there rather than socializing (although that would probably be with a necro anyway), and I've never seen a demonstration. Too much work, I guess. Apart from the omni temple, I've never made one since I haven't had any petitions for them and been busy dealing with more important issues.
As far as I understand the taverns are the places where dorfs are supposed to socialize and make friends.
When it comes to visitors, I've struggled in every world to get them in significant numbers to make conquest militias (they have to be throwaway units, as I was able to recall an average of about 1 member from each conquered site, out of a squad of 10), and I also struggle with getting gobbo, and, in particular, elven visitors (the latter come in performance troupes to some extent, but these troupes are FUBARed, so you can't accept their petitions [+petition screen info...]).
I don't know how I'd tell if visitors added a rumor to the civ screen...
And finally DF is crashing very frequently for me, but in a random, non reproducible way. Accessing address 0, -1, other addresses, trying to execute illegal locations. Thus, it's possible to go forward by saving every 5 or so days, with about one crash per step (not using TwbT). I tried with DFHack disabled and it crashed almost immediately one time, after a few minutes a few times, after 40 minutes (with DF halted on a pause for an unknown time), and running for over two months on another session. Crashes seem to happen more often on events (new season, migrant waves), or seconds after pausing events.