I've avoided forcing capitalization in too many places in the SBL rendering because there are often language-specific (or, within English, even dialect-specific) differences regarding what should be capitalized. I think I already enforce capitalization of the first word, though:
```
\starttexdefinition titleemph #1
\emph{\Word{#1}}
\stoptexdefinition
\starttexdefinition titlequote #1
\quotation{\Word{#1}}
\stoptexdefinition
```
If you want the behavior you've described, you can change \Word to \Words in the lines above (in publ-imp-sbl.mkvi). I probably will leave the code as-is, however, as it seems safer to expect the user to provide the desired capitalization in the BibTeX file.
Joey