The bmi scheme has already had additional restrictions placed on it, following the takeover by Lufthansa. This includes increasing the mileage requirements for redeeming in F, an additional mileage charge for redeeming on Lufthansa and significant capacity restrictions (eg no bmi redemptions on any Singapore Airlnes premium A380 seats).
Although bmi miles are easy to earn, they are difficult to spend, though not impossible with a little help from Expert Flyer, and flexible requirements.
Most everyone who has grappled with the call centre will attest to this.
bmi is a great scheme, but it is always good to diversify your mileage portfolio especially between the two major British members of Star and oneworld, as this opens up a range of choices and makes it more likely you can redeem to take the trips you want at the time you want.