Very small I would expect. I bought my 70D in May 2015 and received it on July 2015. I bought it only 1-2 months after it was announced to replace the 60D model at the time. From what I've gathered, that was short lived until early 2016 when it was replaced with the 75kwh battery. So practically less than 12 months worth of sales I would expect.
We became the neglected baster child. All other battery size have a much longer life cycle, such as 60 kwh, 75kwh, and 85kwh.
I didn't expect it to be such short lived. If I had known I would just waited and get the 75kwh for the same price and being able to add 25-30 more miles to the range. Blah.
I wish Tesla would offer option to just add more cell to existing 70 kwh to make it 75 for a small nominal fee. I would pay upward 1k for that benefit. If up to 85 kwh/90 kwh, I would pay upward to 10k for it.