The Future of WordPress: Block Themes and Full Site Editing Explained

For roughly a decade, building a custom WordPress theme was a predictable ritual. You opened up `header.php`, wrote some rigid Advanced Custom Fields (ACF) layouts, and queried the database. If a marketing manager wanted to move a sidebar from the left to the right... they had to submit a Jira ticket and wait for a developer. But with the massive push towards Full Site Editing (FSE) and Block Themes, that era is ending fast.

What is a Block Theme, really?

Simply put, a Block Theme is built entirely out of Gutenberg blocks. Instead of PHP files spitting out hardcoded HTML structure, a Block Theme uses HTML files containing block-markup. The visual editor in the WordPress backend maps 1:1 to the frontend. The header, the 404 page, the archive layouts—everything is a drag-and-drop block that the administrator can visually edit without touching a single line of code.

The real game-changer is the theme.json file. This single configuration file completely centralizes your design system. You define your color palette, typography scales, spacing presets, and layout widths in one place. WordPress automatically generates native CSS custom properties from this configuration, ensuring total visual consistency across every page and every block.

Why should I switch if my ACF setup works perfectly?

Many veteran developers resist Block Themes because their ACF-based page builders "just work." Here is why the industry is forcing the pivot:

• Catastrophic CSS Bloat: Traditional themes load massive `style.css` files on every page load, regardless of what is on the page. Block Themes only inject the exact CSS required for the specific blocks actively rendered on that URL.
• Native Performance: FSE themes regularly score 95+ on Google Core Web Vitals out-of-the-box because they bypass layers of legacy PHP processing that classic themes require.
• Client Empowerment: Non-technical marketing teams can now rearrange entire page layouts, swap hero sections, and update footer content without filing a single support ticket.

Will Block Themes put developers out of a job?

Absolutely not. The job just shifts.

Instead of hardcoding endless page templates for clients, your job becomes curating the editor experience. You will lock down certain block templates so clients cannot accidentally break the layout. You will restrict palette options to strict brand colors. And you will build custom, high-performance React blocks (InnerBlocks) for complex data interactions that core Gutenberg blocks simply cannot handle—things like dynamic pricing tables, interactive timelines, or custom API-driven content displays.

The Bottom Line

The future of the web is empowering the end-user. Block Themes are the definitive architectural shift that finally gives marketing teams the creative control they want, without sacrificing the performance numbers and code quality that developers demand. If you are starting a new WordPress project today, Block Themes should be your default choice.