There are two rumors I have been hearing. The first is that there have been speculative plans for a Mandarin Oriental in downtown Houston. I didn't hear that it would be in this exact location but rather that it would be near Market Square (which this is). The second came from the Chronicle about up to 6 possible downtown towers on the boards. One of the projects was stated to be a mixed-use project by Linbeck Construction. The Chronicle didn't narrow down the location but they did say it would be near this area.
So, I am hoping that it is the Linbeck mixed-use project and that it involves the Mandarin Oriental!