Yes, we should be able to Morph skill lines. It can make balancing harder, but the benefits are greater anyway. That way you could increase the amount of builds (stamina and magicka) and make the game even more varied. There's nothing more boring than a game where there's a "build of the month". Also when you morph a skill line you should obviously get the skill points back.
Templari]Aedric Spear[/i can morph into
i]Aedra's Judgment[/i, a skill line focused on dealing damage, or
i]Aedra's Aegis[/i, a more defensive skill line for tank characters, with improved variations of Sun Shield; defensive buffs and passives. Both of these with a fair share of Stamina morphs or even originally Stamina skills with Magicka morphs.
i]Dawn's Wrath[/i can morph into
i]Dawn's Vengeance[/i, with better damaging skills for your Magicka Templar DPS, or
i]Dawn's Retribution[/i, a skill line where you have damage amplifying debuffs and support skills (Like Backlash and Blinding Light) to help your friends in battle. No Stamina Morphs in Vengeance, and two or three stamina morphs in Retribution.
i]Restoring Light[/i can morph into
i]Hallowed Light[/i, a skill line focused on healing and support for Magicka characters or
i]Invigorating Light[/i, a skill line focused on self heals for Stamina/Health based characters.
Dragon Knighti]Ardent Flame[/i can morph into
i]Scorching Flame[/i, it would have ranged fire damage skills for your Magicka DK, or
i]Blistering Flame[/i, a skill line for Stamina characters, focused on close range damage skills and utility ones like Fiery Grip and Searing Strike.
i]Draconic Power[/i can morph into
i]Draconic Bastion[/i a defensive skill dealing with shields, damage reduction and self healing, or
i]Draconic Claw[/i, a long ranged support skill, with a whole set of support and damage skills based on Talons.
i]Earthen Heart[/i can morph into
i]Earthen Soul[/i, becoming even more defensive, or
i]Earthen Will[/i, a skill focused on long ranged support and damage, based on the skills Stonefist, Ash Cloud and Petrify.
Sorcereri]Storm Calling[/i can morph into a magicka skill line called
i]Elemental Calling[/i, with damage skills that change the element according to your weapon (Fire/Frost/Shock for fire/frost/shock staves, and "magic" damage for all other weapons) or
i]Storm Embodiment[/i, a Stamina skill line based on those npcs that fight close ranged with their weapon imbued in shock magic.
i]Dark Magic[/i can morph into
i]Blood Magic[/i, a skill about offensive and utility skills that may or may not heal or damage you, based on skills like crystal fragments and dark conversion, or
i]Negation Magic[/i, with skills to cancel spellcasting and some crowd control, based on Negate Magic and Encase, for a controller type of character.
i]Daedric Summmoning[/i can morph into
i]Daedric Subjection[/i, with pet skills (also fix pets) and
i]Daedric Defilement[/i, with the ward and damage skills.
And I didn't played NB so I can't really suggest things.