Well, often it is difficult to answer a question such as you have posed; however, in this instance it is fairly easy. If, by the "new system" you mean the Phase II P25 that has not yet happened, there aren't any mobile scanners that can monitor it. The only scanner on the market so far that is capable of handling the TDMA aspect of the Phase II is a hand held, the GRE PSR800.
If on the other hand, you mean the present
TxWARN P25 system (which will change to Phase II in the future) then there are couple of solutions. The Uniden
BCD996XT and the GRE
PSR-600. Both are DIN-E and either come with the sleeve or a sleeve is available as an option. I am not going to recommend one over the other, and suggest you carefully view the capabilities of each. I did not include the RS Pro-197 in the list, although it is virtually the twin of the PSR-600 because RS is notorious for not keeping the firmware updated in a timely fashion and the firmware updates issued by GRE for the PSR-600 will not work on the Pro-197.