Some achievable goals for the near future:
Ending the supremacy of EU law
Prioritise spending of the money the EU would (after the rebate) otherwise keep or tell us how to spend. Better NHS funding rightly seems a very popular proposal
Regain our seat on the World Trade Organisation
Regaining control of our fishing waters
Equality for migrants from anywhere in the world, not automatic priority for EU migrants
Forging trade deals around the world
Nationalise the railways
Also, planning our future is also about avoiding plans that we don't like. Avoiding the negative is a positive move. E.g., planning not to be involved in:
A superstate
An EU army
A distant, undemocratic setup
A system where big business lobbyists are too powerful
An unreformable system
Propping up the euro
TTIP
I expect those in positions where they can make things happen will indeed have compiled proposals for post-Brexit and know how the "nuts and bolts" would be put together. Just because it's behind the scenes doesn't mean it's not happening. And the "plan" won't be presented as a fait accompli, the proposals will need to be approved first.
It's not like a general election where we can vote on a party manifesto. Many of those standing up for either side aren't in politics themselves, and may not be in a position to personally bring about what they've presented as the best future for Britain.
The remainers do not have solid plans. They can't guarantee that they can reform the EU in any meaningful way, that Cameron's so-called "deal" will be upheld, that any vetos will ever be used, that the EU won't destabilise, that we won't have to bail out the euro, or pay EU taxes, that we won't be required to take part in an EU army, become part of a superstate (not yet, but incentives could potentially bring about deals), that the EU won't take control of benefits, the minimum wage and pensions in a way we'd never choose, etc.