I can see two ways to do mergers:
1. Create a new shard with all the dimensions increased by a factor of 4 (currently, each "step" in terms of latitude & longitude jumps 4-5 minutes, so there's room if you wanted to redo the map into 1 step = 1 minute). This option would work best, but is very labor intensive.
a. This will allow the devs to totally redo the server lines for efficiency with modern hardware, and tweak the terrain a bit (the return of overland spawn, even!). Luna, of course, would become a city with multiple rings of streets around the bank, not just one.
b. Allow people to "pack up" their house and characters, and relocate it to the new shard, but the spot the house can be dropped onto in the new shard has to be within 3 degrees n/s & e/w of where it was before, in the same facet. With each clearing effectively being 16 times the acreage as before, it should be near-impossible to place houses to keep other shards' homes from fitting (the only thing that might come close might be castles).
c. All Event stuff would be copied onto the merged shard, locations tweaked slightly if they conflict (fairgrounds, for example).
d. All houses not moved by the players by the deadline for play to stop on the old shards would be moved by GMs to where they can fit, over 1-2 days. This would also allow the deletion of certain problem houses.
e. After all the houses are moved, then people can start placing and resizing (and the number of castle spots will go up greatly).
2. Option 2, convert T2A into its own pair of facets (and redrawn to be less annoying). Share Fel T2A and Ilshenar between shards.
a. Make the Trammel T2A facet open (after terrain changes) to housing.
b. Make the Fel T2A facet several times larger, with more champ spawn locations, and shared by all Shards at that server farm that use the same ruleset. Add a couple more NPC zones (with guards), and replace the current tunnel/teleporter system with moongates (you still can't recall or gate there) - and put heavy non-champ monster spawns around the towns, making getting to and from the exits just as perilous as the current dungeon entrances can be, and with PvP choke points along the way (only the choke points will have their monster spawns for both sides to deal with).
c. Ilshenar gets expanded and shared the same way. Reds given the ability to enter and leave Ilshenar, but facet would only allow PvP within an alliance/guild, between warring groups, and between factions.
d. Easier done, but might require a "cooldown" time between entering a gate and arriving/departing a shared facet, to prevent bugs and exploits that could dupe things or blackhole characters. While in a gate, characters could not be attacked, attack, or see or be seen by those outside the gate at either end, once the transfer starts.