I'm not saying that everything that is tied to Res/Mag or Initiation/Submersion Grade needs to be capped, I'm simply cautioning that some things should be bounded. Dice pool bonuses from metamagics tend to be limited to very limited tests such as hiding your signature, with the exception of (Adept) Centering which is potentially one of the best metamagics there is for that reason, though Drain is something unique to Awakened that mundane characters don't have to deal with. Shielding is also an obvious exception, but since it isn't applied to every roll it isn't quite as simple as calling it a dice pool bonus. None of the metamagics apply to dice pools or attributes that allow a mage to be better than a mundane at mundane things. For the technomancer you have to be wary of an Echo providing a bonus that makes her better than a decker at things that both can do - slightly better is fine, but significantly better without bound is not.
So, allowing Echoes to increase Matrix attributes is fine, but it needs to be bounded similar to how Physical and Mental attributes are.
With those caveats in mind, lets look at metamagics tied to Initiatiate Grade and/or Magic:
(Adept) Centering: Affects dice pool, no limit. This is the big exception which is not a significant problem as it allows the mage to overcome a weakness that is unique to Awakened, not provide a larger dice pool for something that Mundanes can do. Also, it is needed in order for a mage to be able to keep up with the increasing drain from more powerful spells, which are part of their advancement (the higher your Magic, the more powerful spells you can cast, incurring more drain).
Fixation/Masking: adds to dice pool, no limit. This again allows the mage to overcome a weakness that is specific to them and only affects other mages (or other astral denizens). It does not provide them a notable advantage over mundanes.
Spell Shaping: Tied to Magic Rating, and applies a -1 penalty to casting pool for each meter of change. In all, this could probably be a base mechanic and not be unbalanced due to the high cost incurred when using it.
Infusion: Tied to initiate grade and magic, no limit. The drain cost and GM selected power point loss balance this quite nicely, however.
Shielding: Affects dice pool, no limit. This is just plain good, but again only affects other mages/astral entities. It does not help the mage at all against mundanes.
QI sculpt: tied to initiate grade, no limit. A somewhat unique case, but it doesn't add power - it basically allows a Decker like swapping of points.
Air Walking: not a dice pool, but an effect based on initiate grade. Eventually the Adept can jump for kilometers - look out bad guys! Or any other Awakened could just learn Levitate.
Supernatural Prowess: Tied to magic and initiate grade, limited by the usual +4 limit to attribute enhancement.
Apex Predator: in some settings, this could be god-like. 99.9% of Shadowrun is not that setting. It's up to your GM to allow it in the remaining .1%.
...and so on.
All I'm suggesting is that you consider what impact it has tying an Echo's progression to Submersion Grade if the Technomancer is, say, Grade 10. Does it make him unstoppable or unbalancingly powerful? If so, put a cap on it.