Cons:

No Seasonal Rewards: Miss out on the Season’s Journey, battle pass rewards, and exclusive seasonal content.
Limited New Features: While some updates are applied, you won’t experience the full suite of seasonal mechanics and content.
Season 4 Considerations
Season 4 Specifics:

Loot Reborn: This season focuses on Diablo 4 Items enhancing loot across the board rather than introducing new mechanics. These loot improvements are applied to both realms simultaneously.
Unique Content: Although the major seasonal mechanics are not present, there are still some new features like additional story elements and seasonal currency.
Recommendation:

Try the Seasonal Realm: If you're interested in exploring the latest loot changes and participating in seasonal content, the Seasonal Realm offers the most current and engaging experience.
Stick with Eternal Realm: If you prefer to avoid seasonal changes, continue with the Eternal Realm to focus on your existing characters and complete ongoing campaigns.
Key Points to Remember:
Realm Exclusivity: Characters in the Seasonal Realm cannot play with those in the Eternal Realm and vice versa.
Friends and Co-op Play: Coordinate with friends on which realm to choose if you plan to play together.
Ultimately, the choice between Seasonal and Eternal Realm depends on your interest in new seasonal content and mechanics versus your desire to Diablo 4 Items for sale continue with established characters and core gameplay.