Well, let's take a look:
The properties at 2115 Argonne (13,500 sq ft) and 2415 Mimosa (32,000 sq ft) are owned by the same entity and are both being vacated by December 1. The letter to the residents at 2415 stated that the property had reached end-of-life and would be redeveloped, but did not say how.
The combined lots are actually larger than 2229 San Felipe (36,200 sq ft), but I agree that the odd shape makes an unlikely candidate for a high-rise. I expect that some sort of "Chateau Twenty" will eventually loom over the properties on Avalon Place, and perhaps more interestingly (for the sake of neighborhood drama), block the downtown views of the lowest few floors of the Huntingdon.
The HCAD map facets label these properties as Dickey West Park and Meyers Court, respectively, so I believe they're outside of Avalon Place and would not be subject to the latter's height restrictions (if any). Does anybody have more information?