August to March is 7 months, not 8. I've never waited less than 4 months on a VW factory order - going all the way back to 1989.
To be fair to your dealer, it probably isn't his fault, it's VW's manufacturing schedule. Doesn't mean you shouldn't ask for something back, whether it be money or an equivalent car on loan. It seems reasonable to me since delivery date is a part of the conditions of sale.
Just don't go in there all angry, but go with a few options for them to consider, things which you would find acceptable as compensation (loan car, free servicing for 3 years, free optional extra, etc). Start a little high with what you expect and be prepared to haggle. Leave it with them to consider for a day while you 'think about cancelling the order'.
Give the dealer a chance. If you don't get any joy, then go to VW.