will freedom ever be reached?

Mukuro's situation is very interesting and like he himself says, it's rather ironic. For someone that's been bruised by the mafia for so long and failed at getting his revenge, he's rather calm and accepting of the disposition in being a Vongola guardian. He may not be comfortable with being associated with the Vongola, but this is a fate he has to accept in order to survive (and for Ken and Chikusa to survive). Mukuro hasn't given up on life just yet - he still does plan on taking Tsuna's body for himself. In my opinion... sometimes I'd think it's somewhat of an empty threat. While he has better access to Tsuna by being a Vongola guardian, there's no way that the other guardians (especially Gokudera) would stand for it. It's too much of a burden, at this point, to go through with that action. The other Vongola family members know about his situation (and what he wants to do).

If he's such an 'empty threat', then why is he still in prison? Because he's ex-Estraneo, he attempted to take Tsuna and the Vongola, attacked the Vongola family directly, and escaped from prison once. Clearly if those charges weren't enough to be a "life in prison" factor, then I don't know what is for the mafia. He's clearly a dangerous individual if he's able to use his own body to get out, the mafia/Vendicare prison knows that, that's why he's now in a test tube. The only way for him to 'get out' is to use other people and materialize from them: Chrome Dokuro and Leo (a Millefiore subordiante, ten years later). He's still very much a threat but nothing like he was when he was out of that test tube, haha.

I don't think that Mukuro will reach freedom anytime soon, unless someone wants to infiltrate the "impregnable" Vendicare prison and the deepest, darkest cell down where light cannot reach, then sure? For the most part, I'm not actually sure if Mukuro is released to the wild after Tsuna takes his place as Vongola X in the Future arc. I imagine he isn't out of there quite yet since he still has to materialize into someone else beforehand. For a fan, it's easy to accept Mukuro and forgive him for torturing Tsuna - we see through Tsuna's eyes. Mukuro isn't entirely as evil as the mafia claims him to be [he's still looking out for Ken and Chikusa], but adding up all the things he's done to the strongest mafia around, he's facing serious criminal consequences and he already has a freedom. He's allowed to live (beacuse the mafia sees him has useful - he is allowed to stay alive in the test tube).