I have to say this wound end up being a bad idea long term for a few reasons.

All the reasons mentioned prior are good reasons to not allow multiples. There
are also some others:
Exp plaque gets flooded with people who can grind exp faster. So instead of
Maximus being #1 on place he's 1 and 2? That will affect things like who can
use holzes etc minor yes, but should still be a concern. It also affects how
much exp is just in the game. People already say to much available and exp
pool/power hour/explore etc made things to easy so why basically double the
amount of exp in game?

Sales channel will be even less used. Why would you sell anything that may be
possibly used by your secondary since it reincs every week instead of 1x year?
Keeping all that lower end gear that you'd normally sell/toss gets saved.

Another thing to look at is why would this happen? So highbies have another
option to play? This seems like the worst possible reason to do this. If your
so bored that you need another character to play maybe just *MAYBE* its time
to play real life for a bit. The people this is going to benefit the most are
those same people that say things like Tiamat or GMT are to easy to kill and
everything needs to be tuned bigger/meaner/harder. (This is not a shot at
those people just my opinion). I mean really how many different people have
killed some of these higher end mobs? 50? 100? out of what 5000 unique
players? Why make it so these parties work easier which ironically is the only
good reason for this to be implemented. Parties at night are stupidly hard to
find at times.

Personally I think the better option would be to start blurring the lines on
backgrounds a bit more. I have seen a few people that are getting into guilds
out of background (assume its from wishes or other devious ways) and while
strong if controlled a bit wound not be "broken" and some that would end up
making a bit of sense. This would also allow more diversity without the influx
of other problems.

All in all i would say no to multiple characters. I don't think it will fix
anything and cause a few more headaches than it will be worth long term.
Kanis

PS Since i dont want to edit this post. How does it affect balance when same 9
people can do personal prot mob twice in a row instead of waiting required
days (specially if names share on all pieces). I know the response is prot
itself would have to change, but why should it?