Useful for isolated pockets of vehicles for sure but not a panacea I think.
The space and energy required, not to mention the limited supplies of material to digest (including its transport in the equation) mean that it will be impossible for every home to have one.
How much Methane is this plant producing? How many vehicles will it run?
What is the real cost in terms of space and energy used in getting the whole deal there and distributing the product, then removing the waste? How much energy is used in planting and harvesting crops that are purpose grown for Methane production? How much habitat would have to be cleared worldwide for it to be viable?
Problem is that we have had a cheap and easy ride with fossil fuels (Methane included) for too long to get real about it yet, until Oil and Gas has almost gone that is.
My money is on the simplest thing of all - H20.
Split the H20 (Hydrogen and O2). Burn the H (oxydise it) and produce...H20. Not that simple in reality of course, some energy has to be put in at the beginning to make the split, but enough is around for free if we want to look for it. We will when we have no choice.
Major problems - How does a government tax that? What excuse would they use? It won't be Carbon emissions! Perhaps we'll see a return of the 'Window Tax' and people will rush to buy Vans....!
Seriously though, Science and Technology do not provide us with the limits. Governments with needs for taxation and keeping the masses controlled (read employed) along with private industry and its taste for maximum profit do that much more effectively, Viz. it won't happen until it can be taxed, controlled, monopolised.