A client currently owns two websites. They want to take the content from Website B and move it to be located on Website A's domain name for SEO value. What they want to do is simply to take Website B and move it to a subfolder on Website A then interlink the two websites, taking advantage of Website A's domain authority and Website B's user engagement, low bounce rates and higher quality content.
I would think that Google may take issue with a "merged" Website A/B where half of the site is one template using one CMS, having certain SEO tags, certain HTML structure, etc where the other half of the site is using a completely different template with a different CMS with different SEO tags, different URL structure etc.
My question is whether we can expect any SEO penalties, drawbacks from adding all of this content to the new site with a completely different design/template.