Nakata,
"If Jet2 launched Bournemouth to Barcelona, Ryanair would simply offer all seats free until people get the message that Ryanair fares are the cheapest. Jet2 then would be painfully shown that to mess with Ryanair is a mistake."
Yet LPL has room for FR to do REU and GRO, with EZY doing BCN (x2 iirc). I would be more interested to see if Jet2 could make the slots work at BCN, as this has been commented on quite a few times.
For a weekend city break, people will always prefer to use the airport which can get them where they want to go within 60 minutes of landing (taxiing permitting), whereas REU and GRO serve plenty of other nearby resorts in their own right.
I very much doubt that ticket prices would be the most important issue if J2 were to launch this route.