I thought about this for my shop (2520sf), and ran some rough numbers. It just didn't seem worth it.
First, in this area (Stuntman is close by) there just isn't enough heating days in a season. Just a few months you need heat, and compared to up north, not that big of a temp rise. If the shop is 50, I am happy. Doesn't take much propane in a torpedo to do that. I will go for a couple of weeks or more without spending any real time in the shop. With the radiant, you can't just turn it on and go to work a half-hour later...you have to keep the slab warm all the time. Of course, you'll be living in the same space, so that's different.
Only other thing I can think of is that before the PEX is laid, you'll have to know where you are going to place machinery and equipment NOW, for any and all equipment you have or might get in the future that needs bolted down. IIRC, for something like a 2 post lift, you can't have the pex anywhere with in X feet of the post anchors.
For me, I use a couple of LP space heaters. Long-term plan is to put a gas furnace in. My shop is divided into 3 partitioned areas...I plan to put the furnace where the walls intersect, and dump a dampered vent into each area. Might eventually put a mini-split in the welding room, or the loft if I ever build it enclosed, so I have a cool spot to piddle on really hot days. I have also thought about a passive tin-can solar array to help keep it above freezing, at least.