The expansion of Thomas land onto the carpark was spoken about a few months ago, however I don't believe they will re-theme the old Robinson land rides considering the park sold them to other parks at the end of the 2007 season, plus most were similar versions to what they added in the original Thomas land.
A far as I know a new coaster is still planned in the near future for the buffalo site or next to it, the original plan back in 2011 was a Vekoma launch coaster, they might have looked at Mack as well but plans where defiantly drawn up with Vekoma. I am sure the park could get the funding required for a £5m coaster if they wanted, as far as I have heard they have now paid back the £20m loan for the Hotel) plus the park have done very well since Thomas land and the hotel also does good business. Plus before the hotel and Thomas land they were able to afford to add rides on a regular basis such as £3m storm force 10 in 1999, £3m on apocalypse and Golden nuggets in 2000, £1.2m in 2002 on Maelstrom £3.5m in 2003 on Excalibur, 3.5m G-force in 2005 and £5 Thomas land in 2008.