1. The development of Shackles will continue for as long as we have Patreon support, which means the game could potentially continue to get updates for ever, and be gigantic. According to Steam stats it is currently played for 1h 38m on average.
2. Is there going to be a sequel? well that would require Shackles to be completed, see above.
3. When is shackles going to be completed? see above.
4. As for an Android port, we don't get people asking about it that often, so I can't imagine there's a giant pile of people that only have a phone and are waiting to play out games, to justify the large amount of time spent to reconfigure all the art assets to fit the mobile screen resolution size to be able to release an android port. So it seems unlikely.