To me, it sounds more like each individual spell is going to be more flexible, the opposite direction of movement from 3.5, where spells with versatility were separated into different spells with no versatility.
For example, a Globe of Fire spell might have just been an attack before, it can now be used to create a potent, long lasting light source as well. Or a Bigby's Hand spell can now be used to lift objects or move statues in addition to grappling or pushing foes. Or maybe a Phantom Steed can be used to send a ghost steed forward to trample foes in a line, instead of just being used as a mount.
An extremely useful potentiality and one that my campaign/world has employed for a long time, simply based on the Wizard's intention. Of course in my game every Wizard originates from another world and in that world magic is often channeled or controlled by willpower and so the Wizards have the opportunity to modify certain functional aspects of the spell even as it is being employed. Some Wizards even have the ability to eventually morph one spell into another or to create hybrid spells during usage by modifying effects and functions during employment. Of course these abilities cost in other ways. And are often unpredictable in ultimate effect.
The same basically applies to Clerical magic (thaumaturgy) which is based upon Divine
"miracles" and so miracles can change or transform over time, or sometimes during their occurrence. Of course miracles (and magic) often produce strange side-effects or spell functions occur in completely unforeseen ways, not anticipated by the cleric or magic-user.
I think it's a good idea for the game to make use of generally and widely because it makes magic much less
scientific and far
more magical. I'm glad to see ideas about magic proceeding in a better, more interesting, and more functional direction.
To me, "siloing" means that wizards will have several separate slots (or groups of slots) - one for utility spells, one for offensive spells, and one for defensive spells (for example). In other words, a wizard will have to decide whether to memorize (broadly speaking) fireball or lightning bolt and fly or phantom steed, but he'll never have to make a choice between fireball and phantom steed.
There is no particular reason Sam's idea and a modified version of TB's idea could not be employed conjunctively and simultaneously, magic functioning in both ways at the same time.
This would make all Wizards very powerful, but counter-affecting limitations could be employed to keep it viable and fair (for instance magical employment might draw "unwanted" attention to itself, it might be physically, psychologically - or both - draining, it would be balanced by having monsters and NPC's/enemies be able to employ it in the same way, etc.)