You know this is possible with Bitcoin too (and has much higher impact there), right? It just costs more...

Impact would be on nodes serving historic data, not on nodes validating transactions. Have fun shorting XRP, I'll have fun providing the funds to shorters, collect interest and watch them burn (just look at XRPUSD or XRPBTC market depths and then imagine what happens if a whale decides to make a singe huge buy order to flush out these shorts you put into place around 30 cents...).