As my rent is very low and I have no mortgage, the 14K tax-free would be very positive for me in the short term.If they matched the rent a room relief of first 14k as others have proposed on here, presumably you wouldn't be able to deduct any expenses on the excess, that would be taxed at 52%, so it wouldn't actually work out as a huge saving for me. I'd get an improvement of roughly 1% in yield terms, it wouldn't cover the cost of the risk events above. Personally it wouldn't keep me in, but in conjunction with other measures in terms of control of your property and avoiding regulations that impact on sale value it might.
Reducing the overall tax level to 20% would be similar in that the tax savings would be (very roughly) 1% bump in yield.
So CGT relief for a period of time (5 years/8 years) whatever they deem necessary to encourage investors in the market (existing/new).