Virtual reality is not an acceptable substitute for the Hajj, and it would not be taken as such by anyone. It should be noted that the timing of the Hajj, as with everything on the Islamic calendar, shifts by about two weeks every year. Currently the Hajj is in midsummer, but there will be periods when it is in midwinter, which should continue to be manageable even if some further warming takes place. It is not inconceivable that those years become the only years when the Hajj is possible.
It may also be noted that the Hajj is actually not an absolute religious obligation, even though it is often described in a way that would suggest that it is. In fact, the Hajj is obligatory for those who can afford it, which is an important caveat.Unsurprisingly, for the vast majority of Islamic history the Hajj has been impossible except for a privileged few, and mass access to the Hajj is a basically modern phenomenon. If access to the Hajj were limited by its being made so expensive that the vast majority of Muslims once again found access unfeasible, there would be no inherent problem from an Islamic standpoint.
All that being said, the Sauds' self-proclaimed title of custodian of the holy cities is an important one, and it is responsible for whatever soft power they hold. If they were unable to guarantee access to the Hajj, their prestige in the Islamic world would immediately evaporate. For that reason, massive public works to mitigate the effects of climate are more realistic than any alternative. Whatever expense such a project might entail would be politically worthwhile.
Out of curiosity, how much does going on Hajj cost?
