Pros:
Easier for Staff to manage servers
No more server transfers needed for any reason
Easier to buy mons/can buy mons from "both" servers
No more cross server auctions
Better for PVP Ladder
More people doing ladder so more competition
Better for Guilds having more people in one server
Better balanced prices
Cons:
Reduction of Bosses per Week
Not able to lend mons for with two characters Trainer Tower
EV Training Logout strat could possibly not be faster anymore if there is an extra screen for character selection
Can't safely trade mons/money from 1 character to another
Ideas for Cons:
Implement an account storage for mons and money with the box rework.
Let mons be lendable from the box or implement another functionality to allow mons to go back to their level for trainer tower (people can just ask friends anyway or use another account - it just sucks more to do)
Disable EXP gains in EV-Zones to make Logout Strat become useless