Reminds me of a guy on a steep hill at RAGBREI who casually reached down and pulled a cord --which fired up a well hidden two-stroke engine. He waved goodbye to everyone.
Forgive my negative-nancy comments but,
realistically, having extra weight and super lower gears probably won't be all that impressive. I've often noted fellow riders spinning away in super low gears on a hill as I cranked slowly past them (and some walkers were also walking slowly past them). I did a 600 mi tour on an IGH with deraillers and two front chainrings --to increase the range. Didn't like it at all.
The situation here is I have a vintage (1961 Bianchi) bike with 700C inch rims, 151 BCD Record crank with [EDIT] 50/45T, old Grand Sport short cage derailleur, 120 mm spacing, and 5 speed 14-26T freewheel. The lowest gear now is [EDIT] 47 GI (45x26). The crank will not accept a chainring smaller than 44T. The rear derailleur has very limited chain wrap and max cog capacity. I am thinking about how to get a wider gear range, suitable for randonneuring in hilly terrain, while changing the look of the bike as little as possible, which means keeping the original components as much as possible.
One option, that I am exploring, is to have the crank drilled for a third granny chainring and fit a long cage to the RD. I don't mind the look of a triple, but the Grand Sport RD looks rather odd with a long cage. Cost would be maybe $200 (crank mod, spacers, granny ring, long cage, longer spindle, etc). As always, budget matters. I could get a 37GI with, say, 36 x 26, with gear spacing same as currently.
The other option, discussed in this thread, is to do a hybrid drivetrain. No modification to crank or RD. Upgrades to 8 cogs. But it looks like the frame would have to be spread, a significant negative in my mind. Cost would be maybe $200 (IGH hub if using a CS-RF3, shifter, cassette, spreading). Not counting the wheel rebuild as I'll be doing that anyway (switching to 650B rims). I could get a 41GI (0.75 IGH ratio x 46 x 23T) with closer gear spacing than currently. Adds weight - the Sturmey hub might weigh 700 grams more than the existing Record rear hub, so 1.5 lb gain.
41GI or even 37GI are not impressively low gears, I guess.