Perhaps, but it would be a shred of epic proportions. GAE uses another database project, known as a column-based database, and Django ORM is designed to communicate with relational databases. Since technically everything in GAE is stored in one really large table without a schema (why don't you need syncdbGAE applications), adding custom fields is easy. With relational databases, where each table stores exactly one kind of data (usually) and has a fixed schema, arbitrary fields are not so simple.
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