My agency-side experience has directly put me in front of large-scale migrations and/or replatforming opportunities for several well-established brands. Everything from benchmarking existing organic search metrics, to defining and ringfencing existing SEO optimisation, straight through to the post-launch technical site scans, to speeding up the reindexation of the site.
Here are a some of the considerations that often are overlooked which could save you embarrassment, resource time and money. Existing redirects, have they been included in the redirect mapping stage? You don't want to see drops in organic search visibility caused overlooking existing redirects, same goes for equity devaluing redirect chains.
Have you taken the canonical strategy into consideration? Has the headings been altered, which again could result in a drop of organic search visibility? That also goes for content pruning or forgetting to copy all existing content over.
What this is leading too, I have been involved in numerous platform migrations in varying stages of the process. In each case, I have helped to streamline the processing of the technical and onsite SEO considerations.
I'm certain I could help your team deliver a less stressful website migration or replatforming. Having experience in both Magento 1 & 2, Demandware, Shopify, Wordpress & WooCommerce, Drupal and numerous other platforms.
I could even be the one stays up overnight to monitor the go-live procedure. You wouldn't want to migrate at peak times, would you? I'd hope to think you wouldn't.