Would it be very difficult to add guards and locked doors in houses/castles etc. where there are valuable items? Right now stealing from a Jarl is a joke - no-one cares if I enter into their private bedroom (which isn't locked anyway) and take their gold.

It is even more irritating with mods like Morrowloot which takes high-level items out of loot lists and places them in appropriate locations (mainly with wealthy NPC who can realistically afford it). However, stealing them is so easy it almost defeats the purpose.

An immersive thief experience most certainly requires more obstacles to housetheft than the occasional locked chest.