Jeff Wisnia writes:
You are correct about there being no easy way to just use two off the
shelf slide dimmers to accomplish a soft start from either of two
locations without adding a LOT of complicated electronics.

HTH,

Not really. If you are willing to pay a little extra, Lutron (and
maybe Leviton too) make "smart" dimmers that can be dimmed from either
side of a 3-way switch and remember their previous positions. They
presumably use an X-10 like signalling between the switches to keep
them synced and avoid the problem of two dimmers in "series"