How common is it for new homes to have gas-only dryer hookups?
Around here (Pacific Northwest), electricity is inexpensive and gas is reasonable too.  However, over the last five years, gas prices have declined and will continue to do so and electric has crept up slowly and probably will forever.  Almost all houses here have electric dryers and every single rental (house, apartment, condo) is only electric, even those with gas fireplaces, water heaters, and ranges.

Personally, I like the option of using either gas or electric.  It would not increase the price I'd pay for the house, but it would be one less barrier to moving in.  And that might sway a non-buyer into a buyer.

If it were me, I'd relocate the abandoned wire to be near the new location.  If an unused breaker is actually a problem, just run the wire into the panel full length (so it can be connected anywhere when the time comes) and tuck it out of the way, and secure it, maybe all wires into the neutral strip.  Install the outlet and mark it "not connected".  Place the heavy duty outlet to be semi-accessible so that it could be used by some future high power appliance, like a big air compressor, welder, hot tub, sauna, etc.