Yes, in fact Tokenizer already provides correctOffset which just delegates to CharFilter. We could expand on this, moving correctOffset up to TokenStream, and also adding correct() so that TokenFilters can add to the character offset data structure (two int arrays) and share it across the analysis chain.
Implementation-wise this could continue to delegate to CharFilter I guess, but I think it would be better to add a character-offset-map abstraction that wraps the two int arrays and provides the correct/correctOffset methods to both TokenStream and CharFilter. This would let us preserve correct offsets in the face of manipulations like replacing ellipses, ligatures (like AE, OE), trademark symbols (replaced by "tm") and the like so that we can have the invariant that correctOffset(OffsetAttribute.startOffset) + CharTermAttribute.length() == correctOffset(OffsetAttribute.endOffset), roughly speaking, and enable token-splitting with correct offsets. I can work up a proof of concept; I don't think it would be too API-intrusive or change performance in a significant way. Only TokenFilters that actually care about this (ie that insert or remove characters, or split tokens) would need to change; others would continue to work as-is.
