Working progressive in an interlaced timeline

I have an interlaced timeline

a. because my delivery, although temporally progressive, must be interlaced and

b. so I can step through sources and check if they are indeed interlaced or progressive.

All our acquisition is progressive but much of our archive is interlaced.

Simple, right click on interlaced material and 'deinterlace' (= throw half the vertical resolution away, but whatever)

But, if I speed up *anything* the result is interlaced. Deinterlaced material, sped up = interlaced. Progressive material, sped up = interlaced.

Anyone have any workarounds for this? (mine is to use an adjustment layer with Red Giant Frames doing the deinterlace, or - absent the plug in - to export 'progressive' renders and cut back over the top. )

Really I'd like a 'deinterlace' that worked on interlaced footage post-speed, and an option in the speed dialogue for field/frame based output.