This is a really old skool notion. I'm neutral more than opposed to this; like i imagine most hard core TF2 level designers would be. Personally i thought the visualisers ruined the game visually, as apposed to the spawn sentries in TFC. However the sentries were from HL1 and gave a little tingle from the original game into the back of your mind, of where this game came from, and were also fit to the TFC style (as it was very hl1 texture orientated, along with using the same weapons etc etc). I digress..
My only problem is that the sentries are quite obviously an engineers sentry, and having an invulnerable engineer sentry kind of throws me off. They are also fairly combersum to take into consideration for a spawn.
Personally i would love to see an alternative version to the engineer sentry model used as a spawn defence (such as a single turret minigun implacement, similar in design to the HL1 turret), as it would really bring me home. Plus, anyone who spawn camps deserves a few rounds to the face and a death to their kd ratio, just for trying to get some cheap kills. :closedeyes:
Respawn visualisers are ugly but they do their job. After a single rant on my dissapointment over the lack of imagination put into creating spawn defences i simply let it go and tolerated them. It would be nice to see this go somewhere. But maybe this is a bit much for what you had in mind.