I'll begin by saying an assumption on why the spell was removed (and a possible fix)...
I think they don't want player summoning because of scenarios like this: Let's say a raid ends up being 20 people. Old established guilds will have time to level their mains to the max level and have multiple alts. The developers probably don't want a raid boss to spawn, and suddenly 10 guild members log off, just to log into their elementalist alt to summon 10 other guildies (currently on their mains). And once those 10 main guildies are summoned, they will log off, log in into their elementalist alts and summon the remaining 10 guildies (who were previously on their elementalist alt logging off to log into their mains). This scenario bypasses any restrictions on time limits to cast the spell.
This would create chaos on servers with long established guilds getting to a raid boss or X named NPC first and camping them.
They probably don't care for the normal use of the spell that 99% of the people want it for: ie. if you are in a group, and want to summon a replacement because you or someone else is leaving. They just want to avoid the initial scenario.
Once again, this is just my assumption.
If this is indeed the reason, this could easily be fixed with the following:
-not allowing elementalists to be able to summon anyone X levels above them (say..3 to 5 levels). This would prevent guildies on just leveling elementalists alt to the level they get the summon spell and be done with it. Or summoning a lvl 60 to resolve their problems (ie. camp a mob / harass a player on pvp).
-not allowing elementalists to summon at all (in that zone, or the adjacent zones) for 1 hour once a raid flag is established because a raid event started / boss or named NPC spawned. Lore wise - it could be explained by the mana currents being affected by X mob being spawned preventing summoning (just like evacs can be prevented)
-not allowing the spell to be casted until the elementalist has been online 1 hour (this prevents the fast log off / log in just to execute the summon)
-not allowing the server to execute more than 1 player summon in a zone until 3 minutes pass (if by any chance any of the above fail...it would still take 60 minutes to summon 20 people - giving other players time to arrive and attempt the event as it was envisioned)
I can probably think of other fixes, but since this is just based on an (my) assumption, I'm not trying to overthink it