On BA and QF, don't they give you the option of using many more points to upgrade from Y to J and skip Y+?

Remember this is a long term strategy - it's not something that's going to happen very fast. Yes there may be lots of mileage upgrades right now due to the economy, but if the economy takes off again in 2-3 years time which is the fastest they would roll out a new product, then if the primary motivator is to stop people using miles to upgrade, it would be a short sighted view.