I think the LDs should straight up park their Bus into the hard no-Brexit park. Ultra hard. Straight up reject the Referendum and recommit to the EU, revocation of Article 50 (If this is possible..) - I think they'll get way more voters than they lose.
The Liberal Democrats aren't a national party any more and I think strategically the best thing to do for them is to ignore national political debates. Even if there were loads of 'hard Remain' voters all over the country, and they're looking for a party, they'll look at the last election's results, and realise that the Liberal Democrats are probably irrelevant in their seat, so it doesn't matter anyway. Bluntly speaking, before they can sit at the big boy table, the Liberal Democrats need to rebuild, and get enough MPs together to potentially influence another party; and that rebuilding process means focusing on constituencies on a constituency-by-constituency basis. If they're thinking nationally, they're thinking too big. People don't like wasting votes and until the Liberal Democrats can show they're a real presence again across multiple constituencies, nobody cares what their position is.
What the Liberal Democrats need to do is say: here are our top marginal targets, of which there are 16 they can take on a 5% swing (that is, a 10% shift in the vote). Anything more than that is, in a GE context rather than a byelection, fantasy politics.
If we look at those seats:
Cambridge
Eastbourne
Lewes
Thornbury and Yate
Twickenham
Dunbartonshire East
Kingston and Surbiton
St Ives
Edinburgh West
Torbay
Sutton and Cheam
Bath
Burnley
Bermondsey and Old Southwark
Yeovil
Fife North East
I have bolded the ones which voted Leave, and italicised those which are Scottish. That's 9 out of the Lib Dem's top 16 target seats voting majority Leave (and 9 out of 13 of their English target seats)! Or, in other words: if the Liberal Democrats became the party of Hard Remain, they would almost certainly do worse than if they accepted Brexit and focused on holding the government to account on how Brexit happened.
I think the Lib Dems know this, which is why you have Farron currently trying to have his cake and eat it - bash Labour for being insufficiently pro-EU while having functionally exactly the same policy set. But that's just muddling their message. I think their pro-EU focus is going to hold them back, and my personal prediction for them is about 15-16 seats based on how they're currently performing as a result.
EDIT: also, bluntly speaking, they need more talent. Farron's unpopularity when accounting for DK is comparable to Corbyn's, Corbyn just has a higher profile and therefore a greater number of people aware of him to dislike him. But right now, they have, what, 8 people to choose from, and some of those are even in marginal seats they could then lose, so there's very little choice at all. Again, before they can think big, they need to focus on winning local battles by focusing on local politics until they can find a new leader and a new relevancy.