Maybe 2 second immortality?
And yeah, personally, I enjoyed the chaos of spawning in random points on a map. Plus, I don’t think the dev team will be changing much in terms of original HLDM gameplay, will they?
A 3 second spawn protection seemed to be popular with the server ops in HLDM way back when it was popular. There was a couple of server side mods that achieved this. Nothing worse spawning in game and being killed by 4 trip mine in a row 
immortality no matter how short is a ridiculous way to fix anything in a game with perfectly good walls.
There’d still be a timed death penalty no matter what, so if the server has timed death penalties then it wouldn’t change how fast each player respawns at all, but they can skip the timer if they select a spawn point faster (Making it more frantic, as standard “Penalty” for dying can be frustrating)
However, with instant respawn, it should just be random spawn points.
Server-side should have an option for invulnerability timer, or perhaps a high-armour timer, so they only take 10% damage for the first 3 seconds of spawning.
Area of effect telefragging.
Just kidding.
hahahah, proximity damage based on how close you are to someone who spawns…
but seriously, with model-teamplay, people should spawn near their teammates.