The issue is that BSL no matter how fluent you are in it alone will still mean deaf are reliant on others, on interpreters and on rights campaigns to get even those. You have to aks WHERE, can a deaf adult advance once fluent in BSL? Jobs? More inclusive social interactions? Higher academic attainments? There seems no trade-off between being fluent in BSL, and its effectiveness in a wider 'street' or mainstreamed context.
You could end up with level 6 BSL and still not able to get any job with it, except in a BSL charity or something. Assuming hearing students will then take it up is naive, so many pressures already exist on mainstreamed education, the first question to be asked is, 'what is in it for hearing?' It may well be not as future interpreters, because they are already stating the job isn't economically viable for them, because it is the right thing to do? Hearing have a full list of 127 other minorities and 7 other languages vying for a GCSE class too, where will the hearing find the time? If we are talking numbers, URDU has a higher priority or Polish.
The real key to deaf advancement is TC (Total education), combined with the support that ensures it happens, which means a more realistic focus on how best to enhance real communication effectiveness between the hearing and the Deaf. The only 'awareness' that can succeed, not the 10 best things approach etc.... Perhaps far less emphasis on the suggestion the only social area/future available to deaf people is with their own? That issue has to be addressed day one, if access and inclusion is to be a real option, or even a workable right.
We need also to realise in the UK, the BEST deaf educational establishment is still an oral-based school (Mary Hare). The issue with dedicated BSL classwork is it drives the deaf further and further away from the mainstream of things, and, enhances the deaf activists and cultural segregationists power over the community. While you can agree a majority of the deaf are not fluent in their chosen/preferred language, there is an issue even if they are, because it isn't the language of everyone else and needs 3rd parties to work. This need not be the accepted and fatalistic realism of being deaf, we need to address communication and how it is taught bearing in mind what is more of use.
If the deaf do not, then the alternative is more research into curing and alleviating it all. Bilinguality is a con act as it is, and a deaf world will remain an isolated one.