My problem with all spells as scalable from level 1 on is the Tunnels and Trolls effect. In that game you had a level 1 spells called Take That You Fiend, or TTYF for short. It worked a bit like magic missile or eldritch blast. The problem was that was the only spell some wizards ever cast. TTYF every round, just at different levels. You had a bunch of spells in the book, but you didn't have a bunch of spells being cast.
I feel the same about warlocks and their eldritch blast. It's not that I'm against warlocks or eldritch blasts, it's just that it doesn't feel like a wizard to me.
Having fireball available at 1st level cheapens the spell. I think wizards need something to look forward to. Even if you think that's ok, what about a 1st level meteor swarm? It just doesn't seem right to me and smacks of instant gratification syndrome.
I do think that having a fireball as a 3rd level spells and being able to "pump it up" via meta-magic feats like 3e or with scalable spell levels or with scalable damage depending on caster level like earlier editions feels like D&D, only because spells like fireball have a friendly fire effect...they aren't great all the time. Magic missile is a little more like TTYF particularly being at will, but as long as the damage is lower than prepared spells, it doesn't have the same problem as being the spell that is always cast.
Expanding the list of scalable spells to all spells, or at least all spells that deal damage, is daunting, but probably worth the effort. If you do it for all spells, you can bet that one will rise above the others as being simply better, unless you are careful about the implementation. You have to avoid problems like fireball always being better than meteor swarm, for instance. I think this can be done with damage caps, or by simply paying attention to the math, but thinking through the math to higher levels is something that WotC doesn't have a good track record on, so I agree that they need to add this to the playtest early so we can help.