I actually like this idea. It will give players that are earning points on vanilla something to spend those points on. This way they could buy the AK47, Deagle, P90, FAMAS, etc. The weapons that are already available to the VIPs
I am thinking about this idea for quite awhile. You can only purchased item from pointshop during the preround, that way we can keep people who are rich from purchasing item when they are out of ammo.
You would also have to create a script that if you die pre round, you get that weapon when you spawn. Otherwise, I could prop kill you and you'd be dead and I would get your weapon, leaving you without a weapon and unable to purchase one once the round starts.
You could also have it instead of getting it in preround, you buy it in preround and you get the weapon once the actual round starts, that way you can't duplicate weapons.