The strategy is theoretically viable, in the sense that the AI has no compensation for lost ships (AI Progress excepted, in cases of lost planets, etc, since that eventually causes larger ship volumes in reinforcements and waves). There is no rubber-banding to the AI (ala Mario Kart).
However, I would
somewhat question the premise of a war of attrition against a foe that has 100x your strength, and which tends to build ships faster in response to you, anyway. Generally speaking, even if you have a 200% or better Kill-To-Loss ratio in all of your engagements against the enemy, it will still be gaining ships faster than you depending on the AI Progress level, the difficulty level of the AI, the size of the map, etc.
The difference, of course, is that it is gaining ships across a wider space, and it is severely constrained in how it can use those ships. But because it can focus reinforcements in specific areas, you can cause some "misdirection" of its reinforcements -- and by the same token, it can relatively quickly react to focused threats that you throw against it. So in a sense of whittling down the actual number of units of the AI, I think you'd be fighting a losing battle in pretty much all cases on a galactic scale.
That said, a war of attrition is actually an extremely popular tactic on individual planets. Force fields and other big defenses (superfortresses, etc) cannot be repaired by the AI, but have a very slow regen, for exactly this sort of purpose -- so that you can hit them repeatedly with forces and wear them down over time, if you want/have to. So while I do somewhat question the premise of attrition on a galactic scale because of how the AI functions, when you simply look at a portion of the galaxy, or even an individual planet, I think that tactic is highly effective and actually used by a lot of players (myself included).
Then again, depending on what you feel qualifies as attriting the AI, one could also make the argument that the entire game is founded upon attriting the AI -- not the individual fleet ships, which are simply obstacles to bypass or kill, but rather the larger ships -- command stations, warp gates, ARSes and factories, data centers, guard posts, and so forth. The AI has a fixed supply of those at the start of the game, and they never, ever, get more. Unlike you, they can't rebuild their ships of those sorts that are lost. So as you are expanding into the galaxy, you are putting a permanent crimp into where and how the AI can reinforce itself or how it can attack you.
Another way of looking at it is this: the AI can out-produce you in terms of military ships, and if you try to stem the tide of that galactically, I don't think that's likely to work very well. But on a planet or regional basis, that can work very well, mainly by striking at the reinforcement-affecting ships (command stations, guard posts, warp gates, and special forces guard posts). This sometimes leads to a strategy that players here call "neutering" a planet, which is a form of galactic attrition in my opinion.
Now, all of that said -- is there room for you to do something surprising and original that nobody else has yet done? I think yes.
