All from scratch, and simple hacked together, and untested (cause i should be working ), but can't round-robin be done like this:

What this hopefully should do:
Do a roundrobin with master key '2' and slave-key 'u', on all five wow-instances.

Code:
<command SendAssistToSpecificWindow>
	<SendPC Local>
     	<If ActiveWinIs %3%>
           	 <SendWin %3%>
           	<Key %1%>
     	<Else If ActiveWinIs WoW1>
           	<SendWinM %3%>
           	<Key ctrl shift %2%> 
     	<Else If ActiveWinIs WoW2>
          	<SendWinM %3%>
          	<Key ctrl alt %2%> 
     	<Else If ActiveWinIs WoW3>
          	<SendWinM %3%> 
          	<Key alt shift %2%>
    	<Else If ActiveWinIs WoW4>
          	<SendWinM %3%> 
          	<Key ctrl alt shift %2%>
    	<Else If ActiveWinIs WoW5>
         	<SendWinM %3%> 
         	<Key ctrl %2%>

<Hotkey 2>
   <Toggle>
    	 <SendAssistToSpecificWindow %trigger% u WoW1>
   <Toggle>
    	 <SendAssistToSpecificWindow %trigger% u WoW2>
	<Toggle>
   	 <SendAssistToSpecificWindow %trigger% u WoW3>
	<Toggle>
   	 <SendAssistToSpecificWindow %trigger% u WoW4>
	<Toggle>
   	 <SendAssistToSpecificWindow %trigger% u WoW5>
What i think this should do is the following:

The definition of the <Hotkey 2 ..> does the toggeling, and calls in each toggle the command <SendAssistToSpecificWindow> with the following parameters:

1st parameter: The original pressed hotkey ('master-key')
2nd parameter: The key, which should be pished to the windows which are not active ('slave-key')
3rd paramter: The window, which should the Key be send

..in the Toggle, the last parameter is changed, to simulate round-robin.

<SendAssistToSpecificWindow> does the following:

1. checks if the Window which should the keystroke be send, is the Active window, when this is the case, it sends the unmodified key to it.

When condition 1. is not met, it checks the following for all other windows:
- checks which is the active Window (to know, which modifier combination to send)
- After the active Window is found, send the 'slave-key' with the corresponding modifier to identify the active window, to the Window which is specified by the 3rd paramter

...from pure logic this should work, but as nearly in all software projects, the devil is in the details, so if you chave any thoughts on this, your welcome
Some Flaw might be, that I don't know if this is possible: <If ActiveWinIs %3%> ?!