It's simply way too early ... I could give you my
personal opinion since I saw some people posting expectations about the whole thing where I can only scratch my head... but there is no official information yet apart from what has been announced by now.
The closest thing as to what happens with the input would be in the direction of this
posting from CM SiS in the ENEU section ... apply the differences for US yourself if you will.
In short, it is being read, it will be discussed, but what of it can and will be taken into the actual merges when it comes down to the hard tech is an entire different story.
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My
personal opinion (and keep my signature in mind :p) :
- The merge officially being worked on is a good thing, I don't agree with doomsayers (many of them prevalent on the DE forums actually when it comes to comments about the plans) that this is "the end" - if it would be considered "the end" shutting the whole thing down and grant respective coupons for unused premium currency that has actually been self-bought to use them in other GF games would be MUCH MUCH easier.
- A server merge is certainly NOT the be all end all solution to the problems a game has ... not for other games, not for Runes of Magic. What it does is it brings the players who are still there closer together and creates an overall better gaming experience compared to more servers where everyone feels "alone", even if its not true by the numbers but just a feeling.
- A merge does not solve balancing problems or is a substitution for bugfixing etc - and I know some things have been unfixed for ages. Think I like that? Hell no. I can't fix it myself though

- I'm not even sure how that massive investment (time / resources that could otherwise be used elsewhere) actually "saves" money just because you have to theoretically connect a machine or two less in the datacenter. Sounds neglible in comparison especially since things like hardware are fixed costs that any good business can deduct from taxes ... so it "pays" for itself over time.
- PVP Servers ... quite frankly, and this is my personal opinion ... say goodbye to open pvp servers. If people from servers like Reni and Artemis already go and complain about the lack of population (warranted or not compared to many other servers in the whole of RoM), what in all hell should warrant to keep the PVP servers in the current state? A merge between Grimdal and Indigo? Yeah, right....not.
I too don't see forcing of PVP happening on any of the previous PVE servers either and the only feature of PVP servers that is still actively used is PK-Drop to avoid bind lifters - neither the population nor the remains of the PVP system warrant, in my opinion, to keep ANY of the PVP servers alive - if users of Cogadh/DE or Smacht/EN would ask me the same question they'd get the same answer. But, this is just my personal opinion, I'm not the one who decides any of this, nor the poor sysadmin who has to get all this working in the end 
- total amount of servers after the merge ... tough question. Will Aggropit or Aggropig happen? No idea. I would probably reduce the US side down to 2-3 servers instead of one, but ... we'll know once it progressed and it's not my call anyway

- people who don't want to be merged with certain others because they have personal issues with people on other servers - sorry, if you get merged with $server where such persons are, GET USED TO IT. Nobody gives a damn about personal animosities when it comes to merging servers. This might sound harsh but it's the reality.