It is not only about teleporting, that was just an example, for instance the areaprotection script doesn't support names with spaces and similarly the current areaprotection plugin doesn't too.
Having spaces in names is just a super extra hassle plugin creators have to care for when creating plugins (most of them don't even consider it atm and their plugins do not work with spaces in names) and I don't think it is worth the effort for the 10 people who like a space in their name.
I know this may be out of place, but wouldn't it also be feasible to be able to use the current player ID number from the TAB window? It may need a new plug-in,
yes this is entirely possible and would be an easy fast solution at least for the teleporting problem I think one of the teleporting plugins or scripts did support this at some point but can't remember right now