Conestoga Parkway

[Markster]

There's already a significant amount of space for the on-ramp merge, especially considering how infrequently that on-ramp is used. It certainly isn't a bottleneck or hindrance.

Terrible as it is to say, I think they don't have the cross merge specifically to simplify the transaction for drivers -  this is the on part, this is the off part. Make the lane both, and yeah - you'd get the cross merge slowdown we see on the south side.

Not to mention it would be an extra 500m or so of pavement to maintain, for no real efficiency gain.

It would be about 100m of extra pavement, as that's the distance to fill in between the two ramps.
They already have the Bridgeport onramp continue northbound all the way to University. Clearly such a construction is possible.

While the Lancaster onramp is not a significant source of traffic, it still adds to it. And that makes it the defining bottleneck for the northbound clog. After the 4 lanes merge into 2, it's the one final "oh yeah, let in these extra cars too, before anyone can exit." Connecting the ramps would help grease that section, helping those exiting at Bridgeport avoid a couple minutes of crawling.