It's the second time I heard about this in two days. It's plausible but the roofline isn't very practical for a car with three rows.
Whilst many are talking about the TX, I remain sceptical. "TX" was indeed trademarked by Toyota end of 2010. But it was only trademarked in North America; not in Canada, not in the EU, not in UK and not in Australia. If Lexus had truly planned make a seven-seater SUV, I doubt it'd be available strictly in the US. I'm sure there's potential in this segment worldwide. (Although admittedly, the HS was an example of N.Am and JP only.) Plus, having looked at the trademark database records, it seems like Lexus usually trademarks the specific model name before registering the 'line' (pardon my poor use of terminology). Take the recent LC500/h trademark as an example. Toyota/Lexus didn't trademark "LC" beforehand. They went straight in, and filed "LC500" and "LC500h".
I think this whole thing was just picked up thrown around by Automotive News, 3 years late in 2013.
I'm all pro Lexus three-row SUV, but for now, I can't bring myself to believing in the TX nameplate.
I feel like I will be hated. And when/if I'm proven wrong, I'll be embarrassed - but I'll put my hand on my heart and say, "I was wrong."