Is there any truth to the rumor that Kenwood may be coming out with a second receiver option (hopefully owner plug-in) for the TS-590SG?
No. It would be counter productive to 990 concept. If you do the numbers game though it seems far more likely a new rig is under consideration. There is room for a 490 and a 890 and a 2090 in current numbering. Time will tell.