I'd tend to agree with others that have pointed out siege engines as something that should perhaps be a special case. At the very least it would be important to have the siege workshop have some sort of store of them or allow them to be built in every region type. Otherwise switching from field battle to that big assault against the important city is going to be a way too long process with being able to add only one siege engine "unit" per day. In an army of 30 infantry units that's going to take a long time.
I am not so sure, you know? Clearly depends on how many siege engines with this new system would be assigned to a 30man unit, but as things are now a fully supplied workshop (5 siege engines) would supply 2 and half units in the first day if you assume 1 engine/15 men, and then even less units depending on the production of the region. This opposed to 2 units in a day for every day for what Tom is proposing.
If you consider the average number of men per unit larger (say, 50 instead of 30) the new system would even allow an army to gear up considerably faster I think.
