My team has debated the merits of extendable "bumpers" on several occasions, but we've always ended up deciding that it wouldn't be worth the trouble. Here's a few of the conclusions that we reached.
In order to make such a device fit the current rules, it would have to:
- Start the match retracted within the frame perimeter (because it cannot technically be a bumper if it is articulated in any way)
- Remain within the same height zone that bumpers fit into, so as to avoid being misconstrued as a device intended to contact an opponent outside the bumper zone
- Be constructed from a material which is simultaneously smooth enough to avoid damaging other robots, whilst also being strong enough to withstand multiple, severe impacts
Within these restrictions, my team liked the idea of a 1/4-inch thick sheet of polycarb (or 1/8" thick aluminum, or 3/32" thick steel...), bent into the same shape as the outside edge of a bumper, and with extra bracing as necessary to ensure rigidity. We debated the merits of over-the-bumper deployment versus going through a gap in the bumpers, but ended up dismissing the idea before we came to a conclusion on that one.