I cannot imagine any pools using a windows client to mine, linux would be the choice...
There should be no conflicts on the ix network if a pool uses old builds vs. new ones.
I think an advantage of using the newer code is it might be faster (for things like writing to disk or latency) and in the case of iX the coin control feature is partially crippled (meaning you cannot send what would be one satoshi and set the fee to zero or what would be one satoshi in iX.... this was hardcoded in the source)
The only time a pool 'must' really upgrade is if you make key changes to the source code and using the 'protocol' kick all old clients off the network which is not the case here.
I am uncertain of the status of the other coins merged with bitcoin if they have updated to 9.x level but my guess is no.
If the merged mining is done with eloipool I would not be able to configure it for more than two coins myself and I think attempts to do so with some coins using older and newer codebases might complicate things..... This is speculation on my part I have never ran a pool so others may have the answers.
There is more information here :
https://gitorious.org/bitcoin/eloipool/source/70e71f71a69b48ddf73ef2943f6988422c56c5b9:READMEand here
https://en.bitcoin.it/wiki/Merged_mining_specificationedit 1 a security risk would be running old software that is easier to break into or wallets you cannot lock, for a user who wants to run the full satoshi client (qt) wallet I would suggest using the 9.x codebase. Read the bitcoin wiki and list of upgrades in particular to how 'inputs' and 'outputs' are handled for more detailed information and other reasons the 9.x is superior to prior versions.
Double-Wow!
Thanks to Cinnamon, GroundRod & Ahmed.
Where is GroundRod? Did he not come to receive the honours?
Now Ghash.io has to test merge mining.
Dumb question: what happens if a pool remains on a old version and another move to 0.9.3? Do we benefit of new functionality? Is there any security risk in doing it?
Using eloipool ive been able to get around 5 coins merged mine together all of different versions of the BTC base(although i did rewrite quite a lot of eloipool and the merged mining proxy in the process to fit my needs. Now ive moved to some other code though. waiting for my new server to be brought online for me on monday before i can get to work on getting anything online