You need to embrace N+1 for maximal cycling variety and increased satisfaction.

I don't think you're going to find exactly what you're looking for 'off-the-rack'
If I had to build this bike, i'd start with an early '90s Cannondale, one of the last years with DT shifters, and convert the fork/headset to threadless.

The R/SR's are good all-rounders, the ST's are long, low mile-eaters that can also haul some serious weight, and if you feel like riding your commuter like an express courier, the Criteriums are extra-sporty. Light weight, too by the standards of the day, but still respectable today.

Ironfish: Would you have to convert to 1" threadless? Is there some 1.125 inch headset that have outside-the-frame bearings so you could fit a 1.125 inch fork within the 1" head tube? I ask because full carbon 1.125 forks are so much more common.

I have 2 in my garage right now: '00 Trek 5200 and a '16 Performance generic Al road frame. The former was my first "real" bike; the latter was my son's junior racing bike.

Caloso, have a link to the '16 Performance generic Al road frame, or a picture?

I will have to look.

Well, sorry. It wasn't a 2016, it was a 2014. Here it is as I first built it up with spare parts. Plain white aluminum frame with standard downtube bosses. Unfortunately all the generic AL frames I see out there from Nashbar, Perf, Ribble, etc, now use cable stops with ferrules, so you can't use downtube shifters.

Looks good!

Looks clean.
How is the ride?
Aluminum stiffness is rumored a bit harsh in generic frames, though responsive.

edit: also appears to have clearance for bigger tires. 28mm? they seem big but maybe a visual due to frame size.
re-edit: Oooops = Lithion tires only 23 or 25.

It's probably pretty harsh compared to a carbon frame but my son has no comparison. Also, those Ksyriums are fairly harsh compared to traditional round spoked wheels. Yeah, you could fit 25s, but not 28s.

For $99 (I had a coupon code) it was a great deal. My son has raced on it several seasons, including at Nationals. But he's shot up like a weed in the last year, so I'm going to build up my old Ridley for him. And we'll pass this frame off to another new Junior.

Both my Salsa Casseroll (2010) and my Soma Fog Cutter (2017) had/have 1-1/8" threadless headsets and downtube bosses.

I don't think what you are looking for is hard to find.

I may be mistaken, but I thought that the bosses used for the bolt-on cable stops were the same ones used for downtube shifters.

My 2004 LOOK KG386i has a 1 1/8" full carbon fork and downtube shifter bosses on the frame.

Gunnar still appears to build their frames with bosses: Gunnar Cycles USA, Roadie Road Racing Bicycle