I looked at the price of travel from London to Glasgow earlier this morning for some dates in August. The dates are fixed. The cheapest fare on BA was £189 at times that did not suit me, it was £309 for the times I wanted, steep for economy class travel I thought particularly if I had no status benefits.
The train fare was £150 for times that were suitable so less than half the price to travel at times I want to, that is for first class with proper food and drink v.s. a cup of weak coffee and a miniature biscuit, no aggro from the goons in either direction and no restrictions on what I can have in my bag without having to check it in.
Unless you are connecting to another flight I doubt there is any future in domestic air travel with these sort of prices kicking around.