My company pension scheme tried to use CPI instead of RPI but rapidly threw that idea away when legal advice told them that they would be in breach of the pension contract with scheme members. The Service pension was also linked to RPI and prospective recipients suffered adjustments to salary increases in every annual review to take account of the 'relatively generous pension'.
I believe the government is in the same position as my ex-company in that the link to RPI was a contractual issue not an option.
To those who whinge about the prospect of being worse off in retirement than the present retired community I would merely point out that it was not the older folk who borrowed money that they could not afford to pay back or who sold mortgages to similar people - we learned from an early age that if you could not afford it you did not buy it. Whilst I am concerned that my children might be poor in old age, any reduction in my Service pension does nothing to help me to leave them in a better position.