Down to the final trim work around the hydronic baseboard heaters now. I couldn't go under them so now I have to figure out a way to conceal the 3/4 expansion gap...standard quarter round won't do it and I don't have any way to install a standard base moulding to give me the extra coverage. I knew this would be and issue but didn't want to skimp on the expansion gap, especially with wide plans, hickory, and a fairly wide room. I'm thinking I'll buy some rough sawn hickory and mill out my own custom trim...basically quarter round elongated to cover 1" and nail at and angle so it connects to the sub floor right at the heater's edge.
Got a big bull nose bit? You could bullnose a thick board, then rip it a couple times. Or, obviously, a large roundover bit. No idea how big those are made.
I think I'm visualizing this correctly? the wood was too tall to fit under the baseboard radiators and you want to fill the gap up to the radiators? You've mentioned going to a wood fired boiler in potential future possible plans, meaning you'd probably want the baseboard heaters to function in both radiant and convection properties. Filling that gap will eliminate the convection heat from the radiators. Not to make a renovation take a detour(they all do that on their own) - any possibility of de-soldering the radiators and raising them to the new flooring height?
These aren't typical radiators. Filling the gap won't impede airflow as air doesn't flow through them.
Pictures are easier. Any leftover boards? rip and hit it with a roundover bit using floating blocks underneath with 15x15deg compound miter cuts. You could glue it to the baseboard if desired with a shim on the floor and nail downwards as well Hickory stock has a great variation, using some leftover if you have it will keep things even
Not enough long leftovers...bunch of shorties. This floor has a lot of color variation so whatever I get will match something.
then I'd opt for plan A as you had already - trying to fit a bunch of little 1/4 round trim pieces would detract from the floor. I was thinking gluing up some leftovers to a piece of sacrificial 1/4 ply working the material then shaving the plywood on a tablesaw - might be stable with longer pieces but probably fly into pieces with a dozen little ones
