The problem is ‘substantial impact’ is a subjective term.Who cares? Nobody is subsidising Disabled Railcard holders. Regardless, the expansion of the criteria don't mention that wanting "support or reassurance" will qualify a person for a discount. The criteria will remain exactly as you suggest. From the expanding eligibility page:
With regard to ‘nobody is subsidising Disabled Railcard holders’ , is it established that the income from disabled railcards exceeds the loss from the discount given (allowing for any additional generation of travel)? If not, other passengers are subsidising them.