This add-on is thirty-one lines of code. I made it in five minutes. 70% of that time was finding the variable names. No, seriously, why has no one ever made this? Is there just some form of coder apathy when it comes to extending the default spawnpoint functionality or something?
Whatever. Anyway, about the add-on itself - it introduces a Global Spawnpoint brick. If a player has no spawnpoints themselves and has not used a checkpoint, they will spawn on a random global spawnpoint - if one exists. Otherwise they spawn randomly across the map, as before.
The brick itself can only be planted by admins due to its massive possibilities of abuse if anyone could plant it. This restriction does not apply to loading bricks, but if you have clients loading bricks WITHOUT admin, then you probably have much, much, much bigger problems. Or you don't care either way.