It may not be needed to get up to above 30 000 ft right now, but if all is well and progressing as planned why not try to shorten the flight tests by opening up the flight envelope early, especially if you are on a tight schedule already?
I have the feeling people think the "flight envelope" is somekind of big brown paper envelope that is hard to open with a pair of scissor.
The reality is that you just need to fly into it. Flying and aircraft takes time. For instance the climb can take up to 30 minutes then you flight a more or less level flight and then you descend and land.
One flight is one cycle lost and several hours lost. Knowing that one hour of test flight costs about US$ 120,000 then you do not want to waste money and time when it is not necessary. Please note that the 120 thousand dollars is all inclusive and not just the fuel.
The most difficult part of flight test is NOT flying the aircraft. It is about getting the right data to confirm or to adjust the mathematical model of the aircraft. It also allows to check or adjust all kind small things like slat/flap angle setting, define the different stall speeds with all the final high-lift configuration. The biggest part of flight test is the "low-speed" part (take-off and landing). The other big chunk is calibrating the handling characteristics of the aircraft and then adjusting the flight control system.
Flying at high altitudes is done with clean configuration. Basically you are only getting "high-speed" data like specific air range. It is more about having the efficiency of the aircraft. There is nothing to adjust to the aircraft. If the high-speed performance is not good at that stage, it is already too late to do anything anyway. You need to wait until the next iteration of high-speed aerodynamic iteration.
I just do not understand why so many people are obsessed of flying to 30,000 ft or above when it is just about flying.
We need to understand "Opening the flight envelope" to higher altitude is just flying into it. It is not a kind of tight think and hard brown envelope to cut with a tool.
It is not because you can do it that you should do it.
It is about saving time and money and doing the right thing at the right time.
This recurring question about flying at high altitude during early test flight campaign is so irrelevant that I start to ask question about what those people really have in their mind.