I don't know the answer.
However, I played with Healing Tents on Legends a while ago. You would loose a certain percentage of troops from the Tent every day unless you healed them. i.e. if you did nothing yiou would eventually loose all the troops.
I have noticed if this is in place on Kingdoms....but it is the most logical "solution".
Unknown I guess I was not saying one thing or another. 
It would be a useful function for players who are working together, so from my perspective would be a welcome addition. But some might feel that it detracted from the team collaboration.... i.e. wouldn't need to wait for a player to get online to find out who is attacking them (would make fakes potentially less effective). I guess the number of Viewers could be limited in the same way as Sitters are.
Unknown this is a good idea with little or no impact on the account and would allow new players to see a bigger account.
When you say "alongside sitters" do you mean "in addition" to sitters? In which case it could be used by kingdom members to check each others accounts to see incoming attacks, location of troops, crop situation e.t.c. That would probably have a bigger value than for beginners.
Merging Troops
I played on a Legends "Path to Pandora" server last year that had this function. When merging troops you had to pay the same amount in resources as it cost to build them....i.e.effectively making those troops double the price (bit like a Great Stable/Barracks). Instead of resources you could use Gold but there was a limit you could spend each day (and hence a limit on troop numbers per day). For me, playing mainly def, the cost was not worth it other than to tidy up a few troops here and there (but I am not the biggest Gold spender).
I can see that it would be a more valuable when building a hammer. But I agree that limits should be imposed to avoid the concept of "buying a hammer".
I am not sure how many servers this has been used in Legends but I presume there is some experience / insight around as to how it affected the game play etc.
Fintan, you are correct, it is not neccessarily an efficient use of resources to keep building palaces. There are a few reason why players wish to do this;
1) To switch your capital. Ordinarily players build palace, switch to capital and then leave it but you may wish to switch again later.
2) Chiefing. It is useful to have 3 expansion slots and 3 chiefs in one village when trying to chief a village. Easier / more powerful than sending chiefs from multiple villages.
I am sure there are other reasons too....
Quotethat they can also build some infrastructural elements for the whole kingdom. But what could these elements be? .
What about an "Outpost"? Settled in a same way as a village (limited by culture points or similar etc) but only a holding place for troops. Kingdoms could position them around their area to extend the influence beyond the treasuries. Outposts can be attacked / defended by other Kingdoms to gain /lose area.
