Hyperion's clear preference for its Romantic Piano Concerto series is to couple concertos by different composers.The company is also (understandably) very conscious of commercial imperatives. Coupling two piano concertos by Rubbra would not have appealed to them.
I too am very intrigued to finally hear the early Rubbra Piano Concerto. I have known of its existence for many,many years.
Of course the composer refused to admit it to his canon. Which brings up the old issue about whether or not a composer is in fact the best judge of the merits of his own compositions, particularly the early, "immature " compositions.And in turn the old arguments about our "rights" to resurrect these works, perhapsagainst his expressed wishes.
I doubt whether there can ever, or should be, some general rule. To deny us the opportunity- to pick one example- to hear the majesty and sublime power of Sibelius's "Kullervo" would be an utter tragedy.
So..let's welcome the Rubbra and judge the work for ourselves.
I take what some might regard as a simplistic view of these matters. Rubbra is dead and so he's not going to be affronted. We have to be able to hear the piece to decide whether he was right in his decision to withdraw it. And it's not going to do his reputation any harm either way.