In our branch of Mugai ryu, beginners are expected to separate tameshigiri. However, as you progress, you are expected to perform tameshigiri from the kata. I've found that it has a tendency to change the cuts and aim point a bit.
I feel an important distinction needs to be made between nihonto, traditionally made Japanese swords, and antique or art swords. In Japan, a nihonto is required for tameshigiri as other swords are illegal. As was mentioned earlier, there are a number of apprentices as well as experienced and ranked sword makers that produce user level swords as well as art blades, and expect the iaido community to purchase them, as they won't get purchased by collectors.
Modern made swords, even if they are nihonto, are perfectly acceptable as user swords. Antiques are not, and need to be preserved.
Just my two cents...
Paul