I am well aware of the reputation of HSS for being tedious, but then scraping is tedious. I'm not sure that I have the personality of patience to scrape. I could get by lapping off the machining peaks, or even putting the mill back together 'as machined' and have it work. That is essentially what Seig did when they manufactured it. So, if after some practice pieces, it turns out I'm just way too bored to deal with a scraping project, then I won't have wasted my money setting up to scrape with carbide. I am cheap enough that I would kick myself for not getting that co-ax gauge I've been wanting instead. On the other hand, if scraping is cool, I can set up for carbide and relegate my HSS blade to softer metals. Aluminum bronze gibs come to mind.
My suspicions about diamond wheels was that there would be little migration of carbon at low speed, especially with some coolant. Iron has some interesting phase changes as temperature goes up, so figuring solid solubility and doping levels for carbon into iron is way more than I want to deal with. We had books of diffusion graphs back when I still worked in a silicon foundry, so we didn't even go through the pain of calculation then.
I started sharpening my scraper last night. Connelly talks about polishing off the pits on the side of the blade. I didn't understand where the pits came from until I looked at the commercial HSS blade. It looks like it was sand cast. My previous experience with HSS tools were with ground ones. I would have been happy to pay another dollar or two to have gotten a ground blade. I don't have a course bench stone, so I had to order one. Polishing the flats on my Arkansas stones is painful. I am still wondering how fine a grit I need for honing the HSS cutting edge.