First off, this is the first I'd heard of your mod and I haven't tried it yet so take my opinion with a grain of salt.
I would love a Thieves Guild infinite quest overhaul, and being able to request a target town was much needed. As far as timed missions, it could be very good but the only quests that seem to make sense as time sensitive in vanilla are Shill and Numbers. For the theft missions, perhaps rather than outright failing, having to split your reward with another thief if you don't complete it in time because the guild has to send someone else [flavor, no scripted NPC required], and failure in twice the standard time [because the other thief succeeded]. Like I said though, I haven't seen how you implemented it.
As far as other holds, please do this. My thief tries to pad his activities in an area before he heads out, and having more locations to steal from is always better. Ideally, we'd be able to take more than one quest per giver, but that might break things. I think it makes more sense for a thief to come in and steal as much as possible in a night than it does for things to mysteriously go missing every time he comes to visit.
As far as other quests, there are a lot of things a Thieves Guild does. Some thieves are spies. Some thieves are cogs in the great machine of a Master Thief's plan, skilled at being in the right place at the designated time. Some are dashing rogues whose honeyed words bend everyone to their whim. There are many such jobs that are mechanically identical to the existing quests but with different flavor, allowing for slightly better RP:
Similar to Shill Jobs:
- Helping Hand - Help out a fellow thief by planting some tools of the trade [specific clothes (disguise), lockpicks, potion of invisibility, arrows] in a special container, or unlocking a door, around a certain day and time.
Similar to Burglary:
- Copy Message/Intel - take a document from container, consume charcoal and roll of paper to make duplicate, return document to original container, return duplicate to quest giver
Similar to Fishing:
- Provide False Correspondence/Intel - pickpocket war reports/messages/letters from, and reverse pickpocket falsified versions onto, couriers as they travel between cities (would, by nature, be timed as well) [Whatever the Khajiit caravans use to travel could probably be copied and modified for this.]
Newish Quests:
- Hand off - Not dissimilar to the random encounter where a thief gives you an item to hold on to, except this is guild ordered and you're supposed to bring it back to the guild.
- Distraction - Get within a certain proximity of a thief to alert them to your arrival, then earn a bounty in that area to provide a distraction [no murder], return to guild without clearing bounty. Guild clears your bounty on return. [I think this is the most complex one so far. Hopefully it's not too complex.]
- Persuasion - Persuade someone to slip a lockpick to a prisoner, or leave a parcel somewhere. [These are just persuasion checks plus loss of an item.]
I hope something in there is helpful, and that nothing was overly complex. It's mostly just additional flavor rather than anything new or exciting. But back to the original topic, I'd love to see more holds added and am looking forward to giving your mod a try. /smile.png' class='bbc_emoticon' alt=':)' />