Next will be P38, wait a few more years it will be the L322 in original factory spec without all the added bling, wait another couple of decades it will be the L405.
Like any vehicle, it becomes a 'classic' if it survives long enough and has the four main ingredients : style, rarity, character and that 'certain something' you just can't put your finger on, usually with a Range Rover that's because it'll fall apart if you put your finger on it
Being Range Rover there will always be those of us dumb enough to fall in love with them. In 40yrs a lot of the 'anything with electrics can't be a classic ' brigade will no longer be around. Even some of us with the 'electrics dont stop them becoming classics' brigade, will also be gone and a different generation will be rescuing L322s and restoring them, others will be finding well looked after L405s and keeping them running.
I doubt that in the 1960s or 70s anyone thought a Vauxhall Viva or a Hillman Imp would be classics but they and many of their ilk now are. So people can knock the later models all they like , personally I think that the love of the marque will continue through all variants, (but not all the offshoots). In a few decades it will be a new generation posting on these sites and they will be the ones to decide.