For fun, I'd thought I'd just try and put some quick numbers on profitability.
Based on 2013 September YTD numbers:
BMW Group (including Rolls Royce & Mini) sold 1,436,178 units
BMW Group earned pre-tax profit of € 4,795,000,000 from Automotive business
€ 4,795,000,000 / 1,436,178 = € 3338 average profit per unit
Total X6's shifted since launch to Sept '13 = 226,364
So, 226,364 × € 3338 = € 755,603,032
... Seven Hundred and Fifty Five Million Euros. Or, based on 40k units a year about € 133.5 Million per year.
Now, I appreciate that these numbers are based on simple averages that would seem to include everything from base spec Mini to top end Phantom... but I think they give an idea of why BMW might pursue additional models based on existing platforms - it does seem to make them a reasonable about of money, No?