But one thing you cannot say is the Explorer and 4Runner are similar anymore. Ford's SUV is unibody, IFS/IRS and lacks a low range t-case now. The 4Runner is the last body-on-frame "real" truck-derived SUV and enough people know it. The automotive press dinks Toyota for it, too, being slower handling and all that.
With the elimination of the Cruiser and the way the Sequoia has gone (e.g. IRS, etc.) you have to think even Toyota migh not be that dumb as to mess up mostly owning that segment. Although everyone said Jeep owned their market with the Wrangler and Ford's Bronco is a direct threat to that, the 4Runner, Land Rovers, etc. So maybe Toyota can screw things up worse. Never say never.