In the future, new faiths will be developed and upgraded by their believers.
Open source religions will need several traditional elements, along with a few new ones:

The Founders Effect: the sense of being at the start of an immense adventure. Cult members are poorly informed: for some reason they feel they're the first people this has happened to.

Traditions and anniversaries.

A searchable matrix diagram listing mutually compatible and incompatible beliefs.

Rituals, rites, and restrictions. Paradoxically, religions need a few irrational elements to seem plausible.

New ways for compatible believers to connect online and in real life.

A list of member prophets who claim to know aspects of the ultimate truth, complete with subscriptions.

Subdivisions into factions and sub-factions.

Social projects.

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Probably the best hard SF novel ever written: Infinite Thunder by Jack Arcalon.
Buy the book
Read the chapters