NERC hasn't released their final report so I can only give my opinion from what I've been informed of. They will be able to pull data from every point in the system & analyze it so very well may come to a different, and more accurate, conclusion.
My opinion, take it for what you will:
ERCOT wasn't using an EIM(energy imbalance market). This market, while far from perfect, allows power plants to bid in capacity even when they aren't online. There will be different awards for quickness of availability(15min start, 30min, 1hr, 8hr, 24hr, 48hr etc...). These reserves can then be entered into a program called State Estimator. This program runs continuously & a "study" is run AT LEAST every 30min with actual studies being run every few minutes. During times of trouble, SE can then allow for the dispatching of currently offline generators to pickup lost generation in that region. Downfall is higher costs to the end user.
Again going back to available "backup" generation. Every MW of renewable energy needs to be backed up with either spinning reserve (online reserve capacity or quickstart generators that can be online w/in 15min) and to a lesser extent, standby generators due to their lack of reliability, lack of spinning mass to arrest frequency decline & lack of reactive or MVAR support for voltage control. Either pull some renewables & lower costs or add more spinning reserve/standby generation and increase costs.
Diversify fuel sources. We saw what happened when the natural gas supply fell short. I'm not sure about hydro in TX but if there isn't much coal, biomass, geothermal, solar thermal, fuel oil or other sources available they need to make their main fuel source as reliable as possible. Outside of the low temps causing low pipeline pressures, their gas supply seems good. If most impacted pipelines are above ground installations, heat tracing should be able to be accomplished in just a few years.
Once synchro phasor technologies become more available, power transfer trouble will be able to be predicted much earlier. This wouldn't completely eliminate outages but rather further limit large scale issues by providing more time to react. In all I believe the ERCOT operators on shift did a great job for the cards they were dealt. My largest storm took 187,000 customers(multiply by 2.5 & that's a better representation of people) so I understand the stress. That was just regulated to my desk & not other operators in neighboring areas.
