I still don't understand what you think the benefit is for most users. Having the IAL filled is useless for the vast majority of people who just use mIRC for chatting and don't script. For scripters, 90% of the time when they believe they need the IAL they can actually use $fulladdress and other event identifiers which provide the relevant information when it's most often needed so an auto-filled IAL is redundant. Even when it is needed, as RRX pointed out mIRC still cannot guarantee that the IAL will be filled at any given moment so it doesn't make anything simpler for the scripter - they must still be able to write code that can put in an immediate userhost query (waiting for mIRC to query it itself could be a long time depending on the channel size and where it is in the list) and then write code to do something with the response. Nothing is gained.
As for a continuously updated IAL, I don't really see what users get from that anyway. Knowing which users have IRCOp status is beyond useless, the only thing I can see anyone using that for is trolls knowing when they should behave and when they think the can get away with murder. Knowing the away status of every user on every channel is also, generally, useless (especially when it will only be accurate to the nearest 5-20 minutes). Even when you're speaking in the channel it really doesn't matter what 90% of the users are doing, you'll only ever really be speaking to a handful of users at any one time. For PMs obviously the server will tell you if someone is away, anywhere else the user can append [AWAY] or something to their nick if they think their status is really that important that everyone should know it. The network usage doesn't justify the very limited usefulness IMO.
Even the ISON system for notify lists - which is a great deal less network intensive, is widely considered poor and many networks have dropped the challenge-response method in favour of WATCH lists which allow servers to provide the updates as and when they happen instead of requiring a constant barrage of "are they online yet?" queries from every client. If the away status of users is so important to you you should be bugging IRCd developers about developing some kind of WATCHSTATUS that would have the servers sending a raw for status updates of users sharing channels (or perhaps just ones the user has asked to track - just like WATCH does). Asking mIRC to half-ass a feature on the client-side with an awful implementation method is the wrong way this feature should come about.
