I'm all for seniority based bidding for fleets. There are some very senior members stuck on the 747 who deserve better. Wouldn't it make sense that as you approached your retirement, and after spending many years in the company, you should be allowed to transfer to the fleet of your choice?
Perhaps everyone should be required to have experience on two fundamentally different company aircraft types before a command upgrade? The cross-pollination of skills and ideas would be of significant benefit to both company and individual.
Of course the same can be said about 330 crews who have until recently been taking the brunt of the rostering gamble. Thankfully for them, the 350 is now bringing some relief. Sadly, the 747 fleet crew members don't have that light at the end of the tunnel.