I also looked and couldn't see where it was signed. Maybe the articles jumped the gun, but someone also told me they saw it on the news or facebook this morning which is why I googled it in the first place.
I am personally against allowing rifles during deer season, although I could see it for non-ambulatory people (my brother is one of those for full disclosure). I can see how it looks similar at first blush, but the big difference for me is that allowing rifles doubles (or more) the effective range of the average shotgun which I feel could negatively impact Iowa's deer herd, especially trophy bucks.
Allowing sub-gauges for turkey doesn't do that as far as I can see. Even those TSS loads in 12 ga don't double or triple the effective range of the standard lead turkey loads. My old 835 with lead #5 can kill them all day at 50 yards, I almost never took a shot that far, but it was within the effective range. Most of what I see with the 12 ga TSS is about 70 yards effective range and I have yet to see an article stating they thought that was a shot that should be taken.
My 9 year old niece uses a .410 with TSS #9 in Missouri. It could be years before she can handle the recoil from a 20 ga. I am happy my 8 young nieces and nephews that live in Iowa will have the same option now. I plan on using a .410 myself once it is legal. If you are worried that these 410 TSS loads are underpowered or less effective than 12 and 20 ga loads, below is just one of many articles that you can find disputing that.
Outdoor Life article from 2018
"The .410 put substantially more TSS pellets on the 12-inch target—and in the 6-inch center—at 25 and 40 yards than did the 20-gauge with lead pellets. Yet at 10 yards—where most turkeys get missed—the .410 also threw a broader, more even pattern than the lead 5s, with nearly the same number of pellets striking the sweet center spot.
I didn’t have access to ballistic gelatin for this test, and so I used the next best thing for testing penetration: cans of Showboat Pork and Beans. The cans were no match for lead or TSS at 25 yards. At 40 yards, the lead 5s punched through the front, dented the back of the can, and settled in the beans. The 9s mostly did the same—except for one that passed all the way through the back of the can. I’d have liked a more thorough penetration test, but I’m confident the TSS No. 9s from a .410 don’t give up anything to the lead No. 5s from a 20.
There you have it. The Heavyweight .410 TSS paired with the right shotgun can outperform a 20-gauge with lead turkey loads with a fraction of the recoil. It’ll cost you about $6 a shot. Of course, Heavyweight TSS is available in 20- and 12-gauge too. Might be overkill, but it’s what I’m using this spring.